Wafer holder, heater unit having the wafer holder, and wafer prober having the heater unit

ABSTRACT

A wafer holder hardly deformable under high load and capable of effectively preventing a contact failure with a wafer and further capable of preventing temperature increase of a driving system of a wafer prober is provided. In a wafer holder having a chuck top and a supporter, variation in thickness of the chuck top from a wafer-mounting surface to a contact surface with the supporter, and variation in thickness of the supporter from a bottom surface to a contact surface with the chuck top are both set to at most 50 μm. When the supporter is of a structure having a circular tube portion and a base portion separate from each other, variation in thickness of the circular tube portion from a contact surface with the chuck top to a contact surface with the base portion, and variation in thickness of the base portion from a bottom surface to a contact surface with the circular tube portion are preferably both set to at most 25 μm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer holder used for a wafer proberfor inspecting electric characteristics of a semiconductor wafer bymounting and fixing the wafer on a wafer-mounting surface and pressing aprobe card on the wafer, as well as to a heater unit including the waferholder and a wafer prober including the heater unit.

2. Description of the Background Art

Conventionally, in a process for inspecting a semiconductor wafer, asemiconductor wafer (wafer) as an object of processing has beensubjected to heat treatment (that is, burn-in). Specifically, by heatingthe wafer to a temperature higher than the normal temperature of use,degradation of a possibly defective semiconductor chip is acceleratedand the defective chip is removed, in order to prevent defects aftershipment. In the burn-in process, after semiconductor circuits areformed on the semiconductor wafer and before the wafer is cut intoindividual chips, electrical characteristics of each semiconductor chipare measured while the semiconductor wafer is heated and defective onesare removed. In the burn-in process, reduction of process time isstrongly desired in order to improve throughput.

In the burn-in process as such, a chuck top for holding a semiconductorsubstrate and containing a heater for heating the wafer is used. As theconventional heater, one formed of metal has been used, because it isnecessary to have the entire rear surface of the wafer in contact withthe ground electrode. On a flat plate heater formed of metal, the waferhaving the circuits formed thereon is mounted and heated by the heaterprovided inside, while a probe card having a number of electrode pinsfor electric conduction is pressed on the wafer for inspecting theelectric characteristics of the wafer chip. At this time, an operationof moving a wafer holder on which the chuck top is mounted to aprescribed position by a driving system and pressing the wafer to aprobe referred to as a probe card having a number of electrode pins forelectric conduction is repeated. In the burn-in process, reduction ofprocess time is strongly desired in order to improve throughput.

As described above, the wafer mounted on the chuck top is pressed to theprobe card with a strong force of several tens to several hundreds kgf,and therefore, when the heater is thin, the heater would possibly bedeformed, resulting in contact failure between the wafer and the groundelectrode. Therefore, it has been necessary to use a thick metal platehaving the thickness of at least 15 mm for the conventional chuck topformed of metal, for maintaining rigidity of the chuck top and the waferholder. As a result, it takes long time to increase and decrease thetemperature of the heater contained in the chuck top, which is asignificant drawback in improving the throughput.

In the burn-in process, the chip is electrically conducted and electriccharacteristics are measured. As recent chips come to have higheroutputs, it is possible that a chip generates considerable heat duringmeasurement of electric characteristics, and in some situations, thechip might be broken by self-heating. Therefore, after measurement,rapid cooling is required. During measurement, heating as uniform aspossible is required. In view of the foregoing, copper (Cu) havingthermal conductivity as high as 403 W/mK has been used as the metalmaterial.

In consideration of such problems, Japanese Patent Laying-Open No.2001-033484 proposes a wafer prober using a ceramic substrate that isthin but having high rigidity and is not susceptible to deformation witha thin metal conductive layer formed on its surface, in place of thethick metal plate. It is described that the chuck top having the metalconductive layer formed on the surface of the ceramic substrate has highrigidity and not much susceptible to deformation, and therefore, it doesnot cause contact failure, and in addition, it has small thermalcapacity and hence allows heating and cooling in a short period of time.It is described that as a support base for mounting the chuck top, analuminum alloy or stainless steel is used.

The wafer prober described in Japanese Patent Laying-Open No.2001-033484 above has high rigidity and hardly deforms, as a ceramicsubstrate is used.

As described in Japanese Patent Laying-Open No. 2001-033484, however,when the wafer prober is supported only by the outermost circumference,the wafer may warp when pressed by the probe card, and therefore, it hasbeen necessary to devise measures, such as providing a number ofpillars.

Further, recently, as the semiconductor processes have come to beminiaturized, the load applied per unit area at the time of probing hasbeen increased, and high accuracy of registration between the probe cardand the prober comes to be required. The prober typically repeats anoperation of heating the wafer to a prescribed temperature, moving to aprescribed position at the time of probing, and pressing the probe card.At this time, in order to move the prober to the prescribed position,driving system thereof is also required of high positional accuracy.

There is a problem, however, that when the wafer is heated to aprescribed temperature, that is, to about 100 to 200° C., the heat istransferred to the driving system, and metal components forming thedriving system thermally expand, degrading positional accuracy. This isa cause of a contact failure made more likely during an inspection of asemiconductor chip having a particularly minute circuitry. Further,along with the increase in load at the time of probing, rigidity of theprober itself mounting the wafer has come to be required. Specifically,when the wafer prober itself deforms because of the load at the time ofprobing, uniform contact of the pins of probe card with the wafer wouldfail and inspection becomes impossible, or in the worst case, the waferwould be broken. In order to suppress deformation of the prober, theprober has been made larger and its weight has been increased, posing aproblem that the increased weight adversely influences the accuracy ofthe driving system. Further, as the prober is made larger, the time forheating and cooling the prober becomes extremely long, posing anotherproblem of lower throughput.

Further, in order to improve throughput, it is often the case that acooling mechanism is provided for improving the heating/cooling rate ofthe prober. Conventionally, however, the cooling mechanism has beenair-cooling as described in Japanese Patent Laying-Open No. 2001-033484,or a cooling plate has been provided immediately below the heater formedof metal. The former approach has a problem that cooling rate is slow,as it is air-cooling. The latter approach also has a problem that, asthe cooling plate is metal and the pressure of the probe card directlyacts on the cooling plate at the time of probing, it is susceptible todeformation.

Further, in the prober, stress generated at the time of probing resultsin a load on the chuck top, causing deformation. When the deformationinvolves large deflection, state of contact between the large number ofprobe pins attached to the probe card and the wafer may vary and errorsmay possibly occur at the time of measurement, posing a problem thataccurate evaluation becomes impossible.

SUMMARY OF THE INVENTION

In view of the situations of the conventional art as described above, anobject of the present invention is to provide a wafer holder capable ofeffectively preventing contact failure with a wafer, with deformation ofa chuck top being small even under high load. A further object is toprovide a wafer holder capable of preventing temperature increase in adriving system of the wafer holder, when a semiconductor wafer havingminute circuitry requiring particularly high accuracy is mounted on achuck top and heated. A still further object is to provide a heater unitincluding the wafer holder described above and a wafer prober includingthe heater unit.

In order to attain the above-described objects, the wafer holderprovided by the present invention is characterized in that the waferholder has a chuck top mounting and fixing a wafer on a wafer-mountingsurface, and a supporter supporting the chuck top, wherein variation inthickness of the chuck top from the wafer-mounting surface to a contactsurface with the supporter is at most 50 μm, and variation in thicknessof the supporter from a bottom surface to a contact surface with thechuck top is at most 50 μm.

Preferably, in the wafer holder described above, the supporter has astructure including a circular tube portion in contact with the chucktop and a base portion supporting the circular tube portion, with thecircular tube portion and the base portion separated, variation inthickness of the circular tube portion from a contact surface with thechuck top to a contact surface with the base portion is at most 25 μm,and variation in thickness of the base portion from a bottom surface toa contact surface with the circular tube portion is at most 25 μm.

More preferably, in the wafer holder described above, variation inthickness of the chuck top from the wafer-mounting surface to thecontact surface with the supporter, variation in thickness of thesupporter from the bottom surface to the contact surface with the chucktop, variation in thickness of the circular tube portion from thecontact surface with the chuck top to the contact surface with the baseportion, and variation in thickness of the base portion from the bottomsurface to the contact surface with the circular tube portion are all atmost 10 μm.

Preferably, in the wafer holder described above, ratio of the maximumdiameter to the maximum thickness of the chuck top, that is, ratio ofthe maximum diameter to the maximum thickness (diameter/thickness) is atleast 5 and at most 100. Further, it is preferred that the ratiodescribed above is at least 10 and at most 50.

Preferably, in the wafer holder described above, the material of thechuck top is a composite of metal and ceramics, and more preferably, itis a composite of aluminum and silicon carbide, or a composite ofsilicon and silicon carbide. Alternatively, the material of the chucktop may be ceramics.

Preferably, in the wafer holder described above, the material of thesupporter is ceramics or a composite of two or more ceramics, and morepreferably, it is any of alumina, silicon nitride, mullite, and acomposite of alumina and mullite.

Preferably, in the wafer holder described above, the supporter is formedof a circular tube portion in contact with the chuck top and a baseportion supporting the circular tube portion, thickness of the circulartube portion is at least 0.1 and at most 5.0 with thickness of the chucktop being 1.0, and thickness of the base portion is at least 0.5 and atmost 10.0 with thickness of the chuck top being 1.0. Further, it ispreferred that the circular tube portion and the base portion are formedintegrally.

Preferably, the wafer holder described above has a pillar between thecircular tube portion and the base portion or between the circular tubeportion and the chuck top, and a sum of thickness of the pillar and thecircular tube portion is at least 0.1 and at most 5.0 with thickness ofthe chuck top being 1.0.

The present invention is also directed to a wafer holder having a chucktop mounting and fixing a wafer on a wafer-mounting surface, and asupporter supporting the chuck top, wherein ratio of the maximumdiameter to the maximum thickness of the chuck top is at least 5 and atmost 100.

Preferably, in the wafer holder described above, the ratio of themaximum diameter to the maximum thickness of the chuck top is at least10 and at most 50.

Preferably, in the wafer holder described above, the material of thechuck top is a composite of metal and ceramics.

Preferably, in the wafer holder described above, the material of thechuck top is a composite of aluminum and silicon carbide, or a compositeof silicon and silicon carbide.

Preferably, in the wafer holder described above, the material of thechuck top is ceramics.

Preferably, in the wafer holder described above, the material of thesupporter is ceramics or a composite of two or more ceramics.

Preferably, in the wafer holder described above, the material of thesupporter is any of alumina, silicon nitride, mullite, and a compositeof alumina and mullite.

The present invention is also directed to a wafer holder having a chucktop mounting and fixing a wafer on a wafer-mounting surface, and asupporter supporting the chuck top, wherein the supporter is formed of acircular tube portion in contact with the chuck top and a base portionsupporting the circular tube portion, thickness of the circular tubeportion is at least 0.1 and at most 5.0 with thickness of the chuck topbeing 1.0, and thickness of the base portion is at least 0.5 and at most10.0 with thickness of the chuck top being 1.0.

Preferably, in the wafer holder described above, the circular tubeportion and the base portion are formed integrally.

Preferably, the wafer holder described above has a pillar between thecircular tube portion and the base portion or between the circular tubeportion and the chuck top, and a sum of thickness of the pillar and thecircular tube portion is at least 0.1 and at most 5.0 with thickness ofthe chuck top being 1.0.

Further, the present invention also provides a heater unit for a waferprober characterized in that it includes any of the wafer holders inaccordance with the present invention described above, and a waferprober characterized in that it includes the heater unit.

According to the present invention, in a wafer holder having a chuck topmounting and fixing a wafer and a supporter supporting the chuck top,variation in thickness of the chuck top from the wafer-mounting surfaceto the contact surface with the supporter, and variation in thickness ofthe supporter from the bottom surface to the contact surface with thechuck top are both set to at most 50 μm, and therefore, when electriccharacteristics of a wafer are measured in the burn-in process, thechuck top deformation is small even when high load is applied, andcontact failure with the wafer can effectively be prevented. Further, atthe measurement of a semiconductor wafer having minute circuitry thatrequires particularly high accuracy, temperature increase in the drivingsystem of the wafer holder is prevented when the wafer is mounted on thechuck top and heated, and therefore, positional accuracy between thewafer and the probe card can be improved.

Further, in the present invention, when the ratio of the maximumdiameter to the maximum thickness of the chuck top is set to at least 5and at most 100, deformation (deflection) of the chuck top can bereduced, and therefore, a wafer prober capable of accurately measuringelectric characteristics of the wafer without damaging the wafer can beprovided.

In the present invention, when the supporter is formed of a circulartube portion in contact with the chuck top and a base portion supportingthe circular tube portion, the thickness of the circular tube portion isat least 0.1 and at most 5.0 with the thickness of the chuck top being1.0, and the thickness of the base portion is at least 0.5 and at most10.0 with the thickness of the chuck top being 1.0, a wafer holderhaving high rigidity and superior heat insulating effect can beprovided. In this case, the chuck top deformation is small even when ahigh load is applied, and contact failure with the wafer can effectivelybe prevented. Further, at the measurement of a semiconductor waferhaving minute circuitry that requires particularly high accuracy,temperature increase in the driving system of the wafer holder isprevented when the wafer is mounted on the chuck top and heated, andtherefore, positional accuracy between the wafer and the probe card canbe improved.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic cross-sectional views showing examples of awafer holder in accordance with the present invention.

FIG. 3 is a schematic plan view showing an example of a supporter in thewafer holder shown in FIG. 2.

FIGS. 4 and 5 are schematic cross-sectional views showing examples ofthe wafer holder in accordance with the present invention.

FIG. 6 is a schematic cross-sectional view showing an example of aheater body used for the wafer holder in accordance with the presentinvention.

FIG. 7 is a schematic cross-sectional view showing an example around aportion feeding power to the heater body in the wafer holder inaccordance with the present invention.

FIGS. 8 and 9 are schematic plan views showing examples of the supporterin the wafer holder in accordance with the present invention.

FIG. 10 is a schematic cross-sectional view showing an example of thewafer holder in accordance with the present invention.

FIGS. 11 and 12 are schematic plan views showing examples of thesupporter in the wafer holder in accordance with the present invention.

FIGS. 13 and 14 are schematic cross-sectional views showing examples ofthe wafer holder in accordance with the present invention.

FIGS. 15 and 16 are schematic plan views showing examples of thesupporter and support rod in the wafer holder in accordance with thepresent invention.

FIGS. 17 to 22 are schematic cross-sectional views showing examples ofthe wafer holder in accordance with the present invention.

FIG. 23 is a schematic cross-sectional view showing an example aroundthe portion feeding power to the heater body in the wafer holder inaccordance with the present invention.

FIGS. 24 to 29 are schematic cross-sectional views showing examples ofthe wafer holder in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A specific, basic example of a wafer holder in accordance with thepresent invention will be described with reference to FIG. 1. In thefigures of the present invention, members or portions denoted by thesame reference characters denote the members or portions having similarfunctions unless otherwise specified. A wafer holder 100 in accordancewith the present invention has a chuck top 2 having a chuck topconductive layer 3, and a supporter 4 supporting chuck top 2. A surfaceof chuck top conductive layer 3 is a wafer-mounting surface for mountingand fixing a wafer on chuck top 2. Further, supporter 4 of wafer holder100 is mounted on a driving system (not shown) for moving wafer holder100 as a whole, thus providing a wafer prober.

In wafer prober 100 of the present invention, variation in thickness ofchuck top 2 from the wafer-mounting surface (when chuck top conductivelayer 3 is provided on chuck top 2, from the surface of chuck topconductive layer, same in the following) to the contact surface betweenchuck top 2 and supporter 4 is set to at most 50 μm, and variation inthickness of supporter 4 from the bottom surface to the contact surfacebetween supporter 4 and chuck top 2, that is, variation in thickness ofchuck top 2 and supporter 4, is set to at most 50 μm. With the variationin thickness of chuck top 2 and supporter 4 adjusted to be at most 50μm, deformation and rattling of chuck top 2 can effectively curbed, andcontact failure between chuck top 2 and the wafer can be prevented, whenload is applied by the probe card at the time of measurement.

In the present invention, the ratio of the maximum diameter to themaximum thickness (diameter/thickness) of chuck top 2 may be at least 5and at most 100. In that case, deformation (deflection) of the chuck topcan be reduced, and therefore, a wafer prober capable of accuratelymeasuring electric characteristics of the wafer without damaging thewafer can be provided.

When the ratio mentioned above exceeds 100, chuck top 2 deflects becauseof the load laid by probing, and flatness and parallelism of the uppersurface of chuck top 2 would possibly be degraded significantly. In sucha situation, accurate measurement might be impossible, because ofcontact failure of a probe pin. When the ratio mentioned above issmaller than 5, there would be thermal influence from a side surface ofchuck top 2. Specifically, when the area of an outer circumferentialsurface is too large as compared with the areas of the upper and lowersurfaces of chuck top 2, dependent on the heat balance of the upper andlower surfaces, good temperature control tends to be difficult. In sucha situation, thermal uniformity of the wafer-mounting surface of chucktop 2 deteriorates, and accurate measurement might be impossible. Theratio of the maximum diameter to the maximum thickness mentioned aboveis, more preferably, at least 10 and at most 50. Particularly whenYoung's modulus of the material used for chuck top 2 is 250 GPa orhigher, it is effective to control the ratio of the maximum diameter tothe maximum thickness within the range described above. In the structurehaving a space 5 described above, deflection of chuck top 2 is morelikely because of the applied load, and control of the ratio of themaximum diameter to the maximum thickness is more important.

In the present invention, Young's modulus may be measured, for example,by the pulse method or the flexural resonance method.

Further, it is preferred that the thickness of chuck top 2 except forthe thickness of chuck top conductive layer 3 is at least 8 mm. When thethickness is smaller than 8 mm, chuck top 2 much deforms when load isapplied at the time of inspection and flatness and parallelism of chucktop 2 are deteriorated significantly, causing contact failure of a probepin and accurate measurement would be impossible. Further, the wafermight be damaged. The thickness of at least 10 mm is more preferable, asthe possibility of contact failure can further be reduced.

As other specific examples of the structure of wafer holder inaccordance with the present invention, structures shown in FIGS. 2 and 3may be available. In wafer holder 200 shown in FIGS. 2 and 3, supporter4 has a hollow cylindrical shape with a bottom consisting of a baseportion 41 forming the bottom portion and a circular tube portion 42forming the cylindrical side portion, and by supporter 4 having thehollow cylindrical portion with a bottom, a space 5 is formed in waferholder 200. In the wafer holder having such a structure, most of thevolume of supporter 4 is occupied by space 5 as shown in FIGS. 2 and 3,and therefore, the structure is advantageous in that it has high heatinsulating effect. Further, when base portion 41 and circular tubeportion 42 are separated as shown in FIG. 2, heat insulating effect canbe attained as a contact interface between base portion 41 and circulartube portion 42 serves as a heat resistance. Because of such heatinsulating effect, in addition to the control of deformation andrattling to chuck top 2 described above, reduction in the amount of heattransferred from chuck top 2 through supporter 4 to the driving system(not shown) of the wafer holder can be attained, and temperatureincrease of the driving system can be prevented.

In supporter 4 of the present invention, base portion 41 and circulartube portion 42 may be formed integrally. Here, “formed integrally”means that there would be no slip or gap between base portion 41 andcircular tube portion 42 when supporter 4 bears load. By way of example,a solid cylindrical member may be hollowed out to form base portion 41and circular tube portion 42 integrally. In that case, there is nointerface between base portion 41 and circular tube portion 42.Alternatively, a disk-shaped member for forming base portion 41 and ahollow cylindrical member for forming circular tube portion 42 may befabricated separately and thereafter the two members may be bonded byglass, ceramic paste or the like, to form base portion 41 and circulartube portion 42 integrally. The integrally formed state does not includebodies that are mechanically joined, for example, by screws or clamping.Integral formation of base portion 41 and circular tube portion 42 ispreferred as deformation of supporter 4 is less likely.

When space 5 is formed in the wafer holder of the present invention, theshape of space 5 is not specifically limited, and any shape may beavailable that minimizes the amount of transfer of cold air or heatgenerated at chuck top 2 to supporter 4. It is preferred that supporter4 is adapted to have the hollow cylindrical shape with a bottom, as thecontact area between chuck top 2 and supporter 4 can be made small andspace 5 can be formed easily. When such space 5 is formed, what liesbetween chuck top 2 and supporter 4 is mostly an air layer, and hence,an efficient heat insulating structure can be formed.

In the present invention, when the thickness of chuck top 2 is set to1.0, the thickness of circular tube portion 42 of supporter 4 may be atleast 0.1 and at most 5.0. When the thickness of circular tube portion42 is smaller than 0.1 with the thickness of the chuck top being 1.0,the heat when the wafer is heated may be transferred to the drivingsystem, possibly resulting in thermal expansion of metal components inthe driving system. When the thickness of circular tube portion 42 islarger than 5.0 with the thickness of the chuck top being 1.0, circularportion 42 tends to be deformed more easily.

Further, when the thickness of chuck top 2 is set to 1.0, the thicknessof base portion 41 of supporter 4 may be at least 0.5 and at most 10.0.When the thickness of base portion 41 is smaller than 0.5 with thethickness of the chuck top 2 being 1.0, base portion 41 tends to bedeformed more easily. When the thickness of base portion 41 is largerthan 10.0 with the thickness of the chuck top being 1.0, heatcapacitance of base portion 41 increases as compared with chuck top 2,and therefore, temperature controllability of chuck top 2 would possiblybe lowered and, at the same time, heating/cooling of the heater wouldtake longer time, decreasing throughput.

Specifically, when the thickness of circular tube portion 42 is set toat least 0.1 and at most 5.0 and the thickness of base portion 41 is setto at least 0.5 to at most 10.0 with the thickness of the chuck topbeing 1.0, a wafer holder having high rigidity and superior heatinsulating effect can be provided, in which chuck top deformation issmall even under high load and contact failure with the wafer can beprevented and which can enhance positional accuracy between the waferand the probe card as temperature increase in the driving system of thewafer holder is prevented when the wafer is mounted on the chuck top andheated.

Preferably, the radial thickness of circular tube portion 42 ofsupporter 4 is at most 20 mm. When the radial thickness exceeds 20 mm,the amount of heat transferred from chuck top 2 through supporter 4 tothe driving system of wafer holder may possibly increase. When theradial thickness of the hollow cylindrical portion is smaller than 1 mm,supporter 4 tends to be deformed or damaged more easily by the pressurewhen the probe card is pressed to the wafer, that is, load of the probecard, at the time of wafer inspection, and therefore, the radialthickness should preferably be at least 1 mm. The most preferable radialthickness of circular tube portion 42 is 10 to 15 mm. Further, theradial thickness of circular tube portion at a portion in contact withchuck top 2 should preferably be 2 to 5 mm. In that case, good balancebetween the strength and heat insulating characteristic of supporter 4can be attained.

Further, preferably, the height of circular tube portion 42 is at least10 mm. When the height is lower than 10 mm, the pressure from probe cardacts on chuck top 2 at the time of wafer inspection, and the pressurefurther propagates to supporter 4. As a result, the bottom portion ofsupporter 4 would deflect, possibly degrading flatness of chuck top 2.Further, the amount of heat transferred from chuck top 2 throughsupporter 4 to the driving system of wafer holder may be increased.Further, it is preferred that the thickness of base portion 41 is atleast 10 mm. When the thickness is smaller than 10 mm, the pressure fromthe probe card acts on chuck top 2 at the time of wafer inspection, andthe pressure further propagates to supporter 4. As a result, the bottomportion of supporter 4 would deflect, possibly degrading flatness ofchuck top 2. Further, it is possible that supporter 4 itself is deformedor damaged by the load of probe card. It is more preferable that thethickness of base portion 41 of supporter 4 is 10 mm to 35 mm. Thethickness of 35 mm or smaller is suitable, as the wafer holder can bereduced in size.

In wafer holder 200 having such a structure as shown in FIG. 2 thatsupporter 4 includes circular tube portion 42, in order to maintainrigidity of supporter 4 and to suppress deformation of chuck top 2, itis preferred to set variation in thickness of circular tube portion 42from the contact surface with chuck top 2 to the contact surface withbase portion 41 to be at most 25 μm and to set variation in thickness ofbase portion 41 from the bottom surface to the contact surface withcircular tube portion 42 to be at most 25 μm. In this case also, as inthe example of FIG. 1, variation in thickness of chuck top 2 from thewafer-mounting surface to the contact surface with support 4 must be atmost 50 μm.

In the present invention, when base portion 41 and circular tube portion42 are formed integrally, the contact surface between circular tubeportion 42 and base portion 41 is considered to mean the portioncorresponding to the contact surface between base portion 41 andcircular tube portion 42 shown in FIG. 2.

Further, when every variation in thickness described above is set to atmost 10 μm, deformation and rattling of chuck top 2 can further bereduced. Specifically, in wafer holder 100 of FIG. 1, it is preferredthat the variation in thickness of chuck top 2 from the wafer-mountingsurface to the contact surface with supporter 4, and the variation inthickness of supporter 4 from the bottom surface to the contact surfacewith chuck top 2 are each set to at most 10 μm. In addition, in waferholder 200 of FIG. 2, it is preferred that the variation in thicknessfrom the contact surface between circular tube portion 42 and chuck top2 to the contact surface between circular tube portion 42 and baseportion 41, and the variation in thickness from the bottom surface ofbase portion 41 to the contact surface between base portion 41 andcircular tube portion 42 are each set to at most 10 μm.

In the step of inspecting a semiconductor wafer, heating of a wafermounted and fixed on the wafer-mounting surface of chuck top 2 is notrequired in some cases. Recently, however, it is more often the casethat heating to about 100 to 200° C. is required. Therefore, it ispreferred that the wafer holder of the present invention includes aheater body 6 as shown, for example, in FIG. 4 or FIG. 5. Specifically,when supporter 4 does not have a circular tube shape, a thin cavity 51may be formed at the contact surface of supporter 4 with the chuck top 2in wafer holder 300, and heater body 6 fixed on chuck top 2 may behoused in cavity 51, as shown, for example, in FIG. 4. When thesupporter 4 has the circular tube shape, heater body 6 fixed on chucktop 2 of wafer holder 400 may be housed in space 5 of supporter 4, asshown in FIG. 5.

When heater body 6 for heating chuck top 2 is provided and transfer ofheat from heater body 6 to supporter 4 can not be prevented, the heatwould be transferred to the driving system provided below supporter 4 inthe wafer prober mounting the wafer holder of the present invention, andbecause of difference in thermal expansion coefficient among components,machine accuracy would be deviated, possibly causing significantdeterioration in flatness and parallelism of the wafer-mounting surface(upper surface) of chuck top 2. It is preferred that the wafer holder ofthe present invention has a heat insulating structure such as cavity 51or space 5 described above, because significant deterioration offlatness and parallelism of chuck top 2 can be avoided. Further, it isadvantageous that the wafer holder of the present invention has a hollowstructure with space 5, as weight can be reduced than in an examplehaving supporter 4 of solid cylindrical shape.

As the above-described heater body 6, one formed by sandwiching aresistance heater body 61 with an insulator 62 as shown in FIG. 6 ispreferred, as it has a simple structure. Metal material may be used forresistance heater body 61. By way of example, nickel, stainless steel,silver, tungsten, molybdenum, chromium and an alloy of these may beused, for example, in the form of metal foil, and stainless steel ornichrome is particularly preferred. Stainless steel and nichrome allowformation of a circuit pattern of resistance heater body with relativelyhigh precision by a method such as etching, when it is processed fromthe metal foil to the shape of the heater body. Further, it isadvantageous because it is inexpensive, and is oxidation resistant andwithstands use for a long period of time even when the temperature ofuse is high.

Insulator 62 sandwiching resistance heater body 61 is not specificallylimited, and any heat-resistant insulator may be used. By way ofexample, mica, silicone resin, epoxy resin, phenol resin or the like maybe used. When insulator 62 is resin, filler may be dispersed in theresin, in order to increase thermal conductivity of insulator 62 and totransfer the heat generated in heater body 6 more smooth to the chucktop. The filler dispersed in the resin serves to increase thermalconductivity of the resin. Filler material is not specifically limited,provided that it does not have reactivity to the resin, and a substancesuch as boron nitride, aluminum nitride, alumina, silica or the like maybe available.

As to the method of forming the heater body or the resistance heaterbody, other then etching metal foil described above, a method isavailable in which heater body 6 is provided by forming an insulatinglayer by thermal spraying or screen printing on a surface opposite tothe wafer-mounting surface of chuck top 2, and forming a resistanceheater body layer in a prescribed pattern thereon by screen printing orvapor deposition. Heater body 6 formed of metal foil may be fixed by amechanical method such as screw fixing, on chuck top 2.

When chuck top 2 is heated by heater body 6 and wafer is inspected, forexample, at 200° C., it is preferred that the temperature at a bottomsurface of supporter 4 of the wafer holder is at most 100° C. When thetemperature at the bottom surface of supporter 4 exceeds 100° C., thedriving system of the wafer holder is distorted because of difference inthermal expansion coefficient, and the accuracy would be degraded,possibly causing contact failure, due to positional deviation at thetime of probing, warp or biased contact of the probe caused by lowerparallelism. Further, when measurement is to be done at a roomtemperature after the inspection at 200° C., cooling takes long time andhence, throughput would be decreased.

As an exemplary structure around the portion feeding power to heaterbody 6 of the wafer holder in accordance with the present invention, aportion surrounded by a circle in FIG. 5 of wafer holder 400 isillustrated in enlargement in FIG. 7. At circular tube portion 42 ofsupporter 4, a through hole 44 is preferably formed, and in through hole44, an electrode line 7 for feeding power to heater body 6 or anelectrode line for electromagnetic shield is inserted, as such structureadvantageously facilitates handling of the electrode line. Here, theposition for forming through hole 44 is preferably close to an innercircumferential surface of the circular tube portion 42, that is, closeto the central portion of wafer holder, as the decrease in strength atthe circular tube portion 42 can be minimized. When the formed throughhole 44 is close to the outer circumference of circular tube portion 42,the strength of supporter 4 supporting with circular tube portion 42tends to decrease because of the influence of the probe card, andsupporter 4 tends to deform more easily near the through hole 44. It isnoted that the electrode line and the through hole are not shown infigures other than FIG. 7, for the purpose of simplicity.

A support surface of supporter 4 supporting chuck top 2 shouldpreferably have a heat-insulating structure. The heat-insulatingstructure may be made by forming a notch in supporter 4 to reducecontact area between chuck top 2 and supporter 4. It is also possible toform the heat-insulating structure by forming a notch in chuck top 2. Inthat case, it is preferred that chuck top 2 has Young's modulus of atleast 250 GPa. Specifically, as the pressure of probe card is applied tochuck top 2, the amount of deformation would inevitably increase if anotch is formed and the material thereof has low Young's modulus. Largeamount of deformation possibly leads to damage to the wafer or damage tochuck top 2 itself. Formation of the notch in supporter 4 is preferred,because such a problem can be avoided. As for the shape of the notch, itmay be formed as concentrical trench 21 such as shown in FIG. 8, radialtrenches 22 as shown in FIG. 9, or a number of projections, and it isnot specifically limited.

In the wafer holder of the present invention, supporter 4 may include aplurality of pillars in addition to the circular tube portion. By way ofexample, preferably, a plurality of pillars 23, 43 may be arrangedbetween chuck top 2 and circular tube portion 42 of wafer holder 500,and supporter 4 may be formed by combining pillars 23, 43 and circulartube portion 42 as shown, for example, in FIGS. 10, 11 and 12, as theheat transfer path to the driving system of the wafer holder is madethinner and the amount of heat transferred to the driving system canfurther be reduced while deformation of supporter 4 and chuck top 2 isnot increased. Further, by the provision of pillars, contact interfacesformed between the chuck top and the pillar, between the pillar and thecircular tube portion, between the pillar and the base portion and so onserve as heat resistance, and hence, the amount of heat transferred tothe driving system of the wafer holder can further be reduced.

In the present invention, a plurality of pillars 43 may be providedbetween circular tube portion 42 and base portion 41 of wafer holder 600as shown in FIG. 13.

It is preferred that pillars 23, 43 are in uniform, concentricalarrangement or in a similar arrangement, and that the number is at least8. Recently, wafer size has come to be increased to 8 to 12 inches, andtherefore, if the number is smaller than 8, distance between pillars 23,43 to each other would be long, and when the pins of the probe card arepressed to the wafer mounted on chuck top 2, deflection would be morelikely between the pillars. When the example in which pillars 23, 43 areprovided is compared with the example in which chuck top 2 and supporter4 are integral, provided that the contact area with chuck top 2 is thesame, two interfaces can be formed, that is, between chuck top 2 andpillar member 23, 43 and between pillar member 23, 43 and supporter 4when pillars 23, 43 are provided. These interfaces serve as the heatresistant layers, and hence, heat resistance layers can be increasedtwice as much, whereby the heat generated in chuck top 2 can moreeffectively be insulated. The shape of the pillars 23, 43 is notspecifically limited, and it may be a cylinder or it may be a trianglepole, a quadrangular pole or a polygonal pole with any polygon as abottom surface. No matter what shape, by inserting pillars 23, 43 asdescribed above, the heat from chuck top 2 to supporter 4 can beinsulated. It is noted, however, that regardless of the shape of pillars23, 43, pillars 23, 43 should be arranged in symmetry on supporter 4. Ifthe arrangement of pillars 23, 43 is asymmetrical, it becomes impossibleto uniformly disperse the pressure applied to chuck top 2, possiblyleading to deformation or damage to chuck top 2.

When pillars are provided in the present invention, it is preferred thatthe sum of thickness of pillar 23, 24 and circular tube portion 42 is atleast 0.1 and at most 5.0, with the thickness of chuck top 2 being 1.0.When the sum of thickness of pillar 23, 24 and circular tube portion 42with the thickness of chuck top being 1.0 is smaller than 0.1, the heatwhen the wafer is heated would be transferred to the driving system,possibly resulting in thermal expansion of the metal components of thedriving system. When the sum of thickness of pillar 23, 24 and circulartube portion 42 with the thickness of chuck top being 1.0 is larger than5.0, circular tube portion 42 tends to deform more easily.

It is preferred that the thermal conductivity of pillars 23, 43described above is at most 30 W/mK. When the thermal conductivity ishigher than 30 W/mK, the effect of heat insulation would possibly bedegraded. As the material of pillars 23 and 43, silicon nitride (Si₃N₄),mullite, mullite-alumina composite, steatite, cordierite, stainlesssteel, glass (fiber), heat resistant resin such as polyimide, epoxy orphenol, and a composite thereof may be used.

In the present invention, the thermal conductivity may be measured by amethod such as laser flash method, using pelletized samples.

Perpendicularity between an outer circumferential portion of circulartube portion 42 and the contact surface of supporter 4 with chuck top 2when supporter 4 is formed of base portion 41 and circular tube portion42, or between the outer circumferential portion of circular tubeportion 42 and the contact surface of pillars 23, 43 with the chuck top2 when pillars 23, 43 are provided, should preferably be at most 10 mm,with the measured length converted to 100 mm. For instance, withperpendicularity exceeding 10 mm, it is possible that when the pressureapplied from chuck top 2 acts on pillars 23, 43 or circular tube portion42, pillars 23, 43 or circular tube portion 42 itself tends to deformmore easily.

Further, in the wafer holder of the present invention, it is preferredthat a support rod 8 is provided near the central portion of circulartube portion 42 of supporter 4 of wafer holder 700, as shown in FIGS.14, 15 and 16. FIGS. 14 and 15 show examples in which pillars 43 areformed between chuck top 2 and circular tube portion 42, and FIG. 16shows an example in which the pillars are not formed. By support rod 8,deformation of chuck top 2 when load is applied by the probe card canfurther be suppressed. It is preferred that the material of support rod8 is the same as that of supporter 4, and when base portion 41 andcircular tube portion 42 of supporter 4 are separated, it isparticularly preferred that the material is the same as that of circulartube portion 42. When supporter 4 and support rod 8 thermally expandbecause of the heat from heater body 6 and supporter 4 and support rod 8are formed of different materials, a step would be generated betweensupporter 4 and support rod 8 due to difference in thermal expansioncoefficient, and chuck top 2 would be deformed more easily.

As to the size of support rod 8 described above, it is preferred thatthe cross-sectional area in the radial direction is 0.1 to 100 cm². Whenthe cross-sectional area is smaller than 0.1 cm², satisfactorysupporting effect would not be attained, and support rod 8 tends todeform. When the cross-sectional area of support rod 8 exceeds 100 cm²,the amount of heat transferred to the driving system increases, itbecomes necessary to reduce the size of a cooling module 9 to beinserted in the hollow cylindrical portion of supporter 4 as will bedescribed later, and hence, efficiency of cooling would decrease. Thecross-sectional shape of support rod 8 is not specifically limited, andit may be a cylinder, triangle pole, a quadrangular pole or the like.The method of fixing support rod 8 to supporter 4 is not specificallylimited, and methods such as brazing with an active metal, glass fixing,or screw fixing may be used, and among these methods, screw fixing isparticularly preferred. Screw fixing of support rod 8 to base portion 41facilitates attachment/detachment, and as heat treatment is not involvedat the time of fixing, deformation of supporter 4 or support rod 8 bythe heat treatment can be avoided.

In the wafer holder in accordance with the present invention, supporter4 preferably has Young's modulus of at least 200 GPa. When supporter 4has Young's modulus of at least 200 GPa, deformation of supporter 4 canbe made small, and hence, it becomes possible to support chuck top 2mounted on supporter 4 and to effectively suppress deformation thereof.When Young's modulus of supporter 4 is smaller than 200 GPa, thicknessof the bottom portion of supporter 4 cannot be made thin, and therefore,it is difficult to ensure volume of the space, and hence it tends to bedifficult to attain the heat insulating effect. Further, it tends to bedifficult to ensure a space for mounting the cooling module, which willbe described later. More preferable Young's modulus of supporter 4 is atleast 300 GPa. Use of supporter 4 having Young's modulus of 300 GPa orhigher is particularly preferred, as the deformation of supporter 4 cansignificantly be reduced, allowing further reduction in size and weightof supporter 4.

When supporter 4 includes base portion 41 and circular tube portion 42,it is preferred that base portion 41 and circular tube portion 42 eachhave Young's modulus of at least 200 GPa. When Young's modulus of baseportion 41 is smaller than 200 GPa, it is difficult to reduce thethickness of base portion 41, and it is difficult to satisfactorilyensure the volume of space 5, and hence, it is difficult to expect goodheat insulating effect. Further, when the wafer holder of the presentinvention has the cooling module, which will be described later, mountedthereon, it tends to be difficult to satisfactorily ensure the spacetherefor. It is preferred that base portion 41 and circular tube portion42 each have Young's modulus of at least 300 GPa, as the deformation ofsupporter 4 can significantly be reduced, allowing further reduction insize and weight of supporter 4.

Supporter 4 preferably has thermal conductivity of at most 40 W/mK. Whenthe thermal conductivity of supporter 4 is set to at most 40 W/mK, theamount of heat transferred from chuck top 2 through supporter 4 to thedriving system of the wafer holder can further be reduced, andtemperature increase of the driving system can effectively be prevented,so that accuracy of the driving system is not affected.

Recently, a temperature as high as 150° C. is required at the time ofprobing, and therefore, it is particularly preferred that supporter 4has thermal conductivity of at most 10 W/mK. More preferable thermalconductivity is at most 5 W/mK. With the thermal conductivity of thisrange, amount of heat transfer from supporter 4 to the driving systemdecreases significantly.

When supporter 4 includes base portion 41 and circular tube portion 42,it is preferred that base portion 41 and circular tube portion 42 eachhave thermal conductivity of at most 40 W/mK. When either base portion41 or circular tube portion 42 has thermal conductivity exceeding 40W/mK, the heat transferred to chuck top 2 is easily transferred tosupporter 4, possibly affecting the accuracy of the driving system.Recently, a temperature as high as 150° C. is required at the time ofprobing, and therefore, it is particularly preferred that base portion41 and circular tube portion 42 each have thermal conductivity of atmost 10 W/mK, and thermal conductivity of at most 5 W/mK is particularlypreferred as the amount of heat transfer from supporter 4 to the drivingsystem decreases significantly.

As the material for supporter 4 having Young's modulus and thermalconductivity as described above, various ceramics or a composite of twoor more ceramics may be used. Among these, considering processabilityand cost, mullite, silicon nitride, alumina or mullite-alumina compositeis preferred as the material for supporter 4. Particularly, mullite ispreferred as it has low thermal conductivity and attains high heatinsulating effect, and alumina is preferred as it has high Young'smodulus and high rigidity, respectively. Mullite-alumina composite isgenerally preferred as the thermal conductivity is lower than aluminaand Young's modulus is higher than mullite.

In the wafer holder of the present invention, it is preferred that chucktop 2 has Young's modulus of at least 250 GPa. If Young's modulus ofchuck top 2 is smaller than 250 GPa, chuck top 2 would be significantlydeformed when load is applied at the time of inspection, and flatnessand parallelism of the wafer-mounting surface of chuck top 2 wouldpossibly be degraded significantly. In that case, contact failure occursand accurate inspection becomes impossible, and further, the wafer mightpossibly be damaged. Young's modulus of at least 300 GPa is morepreferable, as the possibility of contact failure can further bereduced.

Chuck top 2 preferably has thermal conductivity of at least 15 W/mK.When the thermal conductivity of chuck top 2 is lower than 15 W/mK,temperature uniformity of the wafer mounted on chuck top 2 would bedeteriorated. When the thermal conductivity is not lower than 15 W/mK,thermal uniformity having no adverse influence on inspection can beattained. Thermal conductivity of 170 W/mK or higher is more preferable,as the thermal uniformity of the wafer can further be improved.

It is preferred that warp of chuck top 2 is at most 30 μm. When the warpexceeds 30 μm, contact with a needle of the prober may possibly bebiased at the time of probing, and evaluation of characteristics wouldfail, or erroneous determination of defects would be made because of thecontact failure. Thus, it is possible that production yield is evaluatedlower beyond necessity.

Further, the parallelism between the surface of the chuck top conductivelayer 3 and the rear surface at the bottom portion of supporter 4 ispreferably at most 30 μm. If the parallelism exceeds 30 μm, the contactfailure describe above possibly occurs. Even when the warp andparallelism of chuck top 2 are at most 30 μm and satisfactory at a roomtemperature, it is not preferred from the same reasons as describedabove that the warp and parallelism exceed 30 μm at the time of probingat 200° C. It is not preferred either, from the same reasons asdescribed above that the warp and parallelism exceed 30 μm at the timeof probing at −70° C. Specifically, it is preferred that at least one ofwarp and parallelism is at most 30 μm in the entire temperature range ofprobing, and further, it is preferred that warp and parallelism are atmost 30 μm in the entire temperature range of probing.

The warp and parallelism may be measured using, for example, athree-dimensional measuring apparatus.

It is preferred that chuck top 2 deflects at most by 30 μm when a loadof 3.1 MPa is applied to chuck top 2. A large number of pins forinspecting the wafer press the wafer from the probe card to the chucktop 2, and therefore, the pressure also acts on chuck top 2, and chucktop 2 deflects to no small extent. When the amount of deflection at thistime exceeds 30 μm, it becomes impossible to press the pins of the probecard uniformly onto the wafer, and inspection of the wafer might fail.More preferably, the amount of deflection when the load of 3.1 MPa isapplied to chuck top 2 is at most 10 μm.

As the material for chuck top 2 having such Young's modulus and thermalconductivity as described above, various ceramics, metal andmetal-ceramics composite materials may be available. Preferredmetal-ceramics composite material include, by way of example, compositematerial of aluminum and silicon carbide and composite material ofsilicon and silicon carbide, which have relatively high thermalconductivity and easily realize thermal uniformity when the wafer isheated. Of these, composite of silicon and silicon carbide (Si—SiC) isparticularly preferred, as it has high thermal conductivity of 170 W/mKto 220 W/mK and high Young's modulus.

As regards the method of forming heater body 6 when a conductivematerial such as metal or metal-ceramic composite is used as thematerial for chuck top 2, heater body 6 may be formed by forming aninsulating layer through a method of thermal spraying or screen printingon a surface opposite to the wafer-mounting surface of chuck top 2, andby screen printing the conductive layer thereon, or by forming theconductive layer in a prescribed shape through a method such as vapordeposition.

Alternatively, metal foil of stainless steel, nickel, silver,molybdenum, tungsten, chromium and an alloy of these may be etched toform a prescribed pattern of heater body, to provide the heater body 6.In this method, insulation from chuck top 2 may be attained by themethod similar to that described above, or an insulating sheet may beinserted between chuck top 2 and the heater body 6. This is preferable,as the insulating layer can be formed at considerably lower cost and ina simpler manner than the method described above. Resin available forthis purpose includes, from the viewpoint of heat resistance, micasheet, epoxy resin, polyimide resin, phenol resin and silicone resin.Among these, mica is particularly preferable, as it has superior heatresistance and electric insulation, allows easy processing and isinexpensive.

Use of ceramics as the material for chuck top 2 is advantageous in thatformation of an insulating layer between chuck top 2 and heater body 6is unnecessary. As the method of forming heater body 6 in this case,methods similar to those described above may be adopted. Among ceramics,alumina, aluminum nitride, silicon nitride, mullite, and a compositematerial of alumina and mullite are preferred as they have relativelyhigh Young's modulus and hence, not much deformed by the load of theprobe card. Of these, aluminum nitride (having thermal conductivity of170 W/mK) and Si—SiC composite (having thermal conductivity of 170 W/mKto 220 W/mK) are preferred, as they have particularly high thermalconductivity and allow formation of chuck top 2 of superior thermaluniformity.

Alternatively, when a metal is used as the material for chuck top 2,tungsten, molybdenum and an alloy of these having high Young's modulusmay be used. Specific examples of the alloy are an alloy of tungsten andcopper, and an alloy of molybdenum and copper. These alloys can beproduced by impregnating tungsten or molybdenum with copper. Similar tothe ceramics-metal composite described above, such metal is a conductor,and therefore, by forming chuck top conductive layer 3 and formingheater body 6 by the method similar to that described above, chuck top 2for use is obtained.

In the wafer holder of the present invention, chuck top 2 may have onits surface a chuck top conductive layer 3. In this case, the surface ofchuck top conductive layer 3 may form the wafer-mounting surface. Whenchuck top 2 is an insulator, chuck top conductive layer 3 has a functionof a ground electrode. In addition to the function above, chuck topconductive layer 3 has a function of earthing that interceptselectromagnetic noise from heater body 6 and the like, and the functionof protecting chuck top 2 from corrosive gas, acid, alkali chemical,organic solvent or water. Possible material for chuck top conductivelayer 3 includes copper, titanium, nickel, noble metal, tungsten,molybdenum and the like.

Possible methods of forming chuck top conductive layer 3 include amethod in which a conductive paste is applied by screen printing andthen fired, vapor deposition or sputtering, thermal spraying andplating. Among these, thermal spraying and plating are particularlypreferred. Thermal spraying and plating do not involve heat treatment atthe time of forming chuck top conductive layer 3, and therefore, warp ofchuck top 2 caused by heat treatment can be avoided and chuck topconductive layer 3 can be formed at a low cost.

Particularly, a method of forming chuck top conductive layer 3 byforming a thermally sprayed film and then forming a plating film furtherthereon is preferred. The material thermally sprayed (aluminum, nickelor the like) forms some oxide, nitride or oxynitride at the time ofthermal spraying, and such compound reacts to the surface of chuck top2, realizing firm contact between the thermally sprayed film and chucktop 2. The thermally sprayed film, however, has low electricconductivity because it contains the compound mentioned above. Incontrast, though contact strength of a plated film with the surface ofchuck top 2 is not as high as that of the thermally sprayed film,plating forms an almost pure metal film, and therefore, a conductivelayer of superior electric conductivity can be formed. The thermallysprayed film and the plating film both contain metal as the maincomponent and, therefore, contact strength therebetween is high.Therefore, by forming the thermally sprayed film as a base and formingplating film thereon, chuck top conductive layer 3 having both highcontact strength and high electric conductivity can be provided.

When the material of chuck top 2 is metal, chuck top 2 itself haselectric conductivity even when chuck top conductive layer 3 is notformed. Chuck top conductive layer 3, however, may be newly formed onthe wafer-mounting surface of chuck top 2, if it is the case that chucktop 2 is much susceptible to oxidation or alteration, or it does nothave sufficiently high electric conductivity. As the method of formingchuck top conductive layer 3 in this case, vapor deposition, sputtering,thermal spraying or plating may be used as in the foregoing.Specifically, a method of applying oxidation resistant plating such asnickel, or a method of forming chuck top conductive layer 3 by thecombination of thermal spraying and plating and polishing the surface asthe wafer-mounting surface may be used.

Chuck top conductive layer 3 preferably has the surface roughness Ra ofat most 0.1 μm. When the surface roughness Ra exceeds 0.1 μm, the heatgenerated from a wafer having a high calorific value during inspectionof the wafer could not be radiated from chuck top 2, and the wafer mightbe heated and possibly be broken by the heat. The surface roughness Raof chuck top conductive layer 3 should more preferably be at most 0.02μm, as more efficient heat radiation becomes possible.

Surface roughness Ra of a contact surface between supporter 4 and chucktop 2 is preferably at least 0.1 μm, both at supporter 4 and chuck top2. When the surface roughness Ra mentioned above of supporter 4 andchuck top 2 at the contact surface is at least 0.1 μm, increase incontact area between supporter 4 and chuck top 2 and relative decreasein gap between supporter 4 and chuck top 2 are prevented, and heatresistance at the contact surface increases. Therefore, the amount ofheat transferred to the driving system of the wafer holder can bereduced. The upper limit of surface roughness Ra is not specificallylimited. When the surface roughness Ra exceeds 5 μm, however, the costfor surface processing tends to increase, and therefore, surfaceroughness Ra of at most 5 μm is preferred. As for the method ofrealizing surface roughness Ra of at least 0.1 μm, polishing process orsand blasting may be performed. In that case, conditions for polishingor sand blasting must be optimized to maintain surface roughness Ra ofat least 0.1 μm.

When the supporter is formed of base portion 41 and circular tubeportion 42, it is preferred that surface roughness Ra at a contactsurface between circular tube portion 42 and chuck top 2 or pillar 23,43 is at least 0.1 μm. When the surface roughness Ra is smaller than 0.1μm, contact area between circular tube portion 42 and chuck top 2 orpillar 23, 43 increases, and the gap therebetween becomes relativelysmaller. Therefore, as compared with the case where surface roughness Rais 0.1 μm or larger, the amount of heat transfer possibly increases.Though the upper limit of surface roughness Ra is not specificallylimited, when the surface roughness Ra exceeds 5 μm, the cost forsurface processing tends to increase, and therefore, surface roughnessRa of at most 5 μm is preferred.

It is preferred that, other than the contact surface between supporter 4and chuck top 2, the surface roughness Ra is similarly set to be atleast 0.1 μm at the contact surface between the bottom surface ofsupporter 4 and the driving system, the contact surface between baseportion 41 of supporter 4 and circular tube portion 42, and the contactsurface between circular tube portion 42 and the plurality of pillars23, 43 when circular tube portion 42 and the plurality of pillars 23, 43are used in combination, as the heat resistance is increased and theamount of heat transferred to the driving system of the wafer holder canbe reduced.

Specifically, when the surface roughness Ra of the contact surfacebetween the bottom portion of supporter 4, that is, the bottom surfaceof supporter 4 and the driving system is at least 0.1 μm, the amount ofheat transferred to the driving system can also be reduced. Further, asfor the surface roughness Ra at the contact surface between base portion41 and circular tube portion 42, it is preferred that at least one ofbase portion 41 and circular tube portion 42 has surface roughness Ra ofat least 0.1 μm. At the contact surface, if base portion 41 and circulartube portion 42 both have surface roughness Ra smaller than 0.1 μm, theeffect of cutting heat from circular tube portion 42 to base portion 41of supporter 4 would possibly be reduced. Reduction in heat quantitytransferred to the driving system, attained by the increased thermalresistance, leads to reduction of power supply to the heater body 6.

When base portion 41 and circular tube portion 42 are formed integrallyin supporter 4 and pillars 23, 43 are provided between supporter 4 andchuck top 2, it is also preferred that the surface roughness Ra at thecontact surface between pillar 23, 43 and supporter 4 and at the contactsurface between pillar 23, 43 and chuck top 2 is at least 0.1 μm asdescribed above. By making larger the surface roughness Ra also atpillars 23, 43, transfer of heat to supporter 4 can be reduced. Asdescribed above, by forming interfaces between various members andsetting surface roughness Ra of the interfaces to at least 0.1 μm, theamount of heat transferred to the bottom portion of supporter 4 can bereduced, and as a result, power supply to the heater body 6 can bereduced.

In the present invention, surface roughness Ra represents arithmeticmean deviation, of which detailed definition can be found, for example,in JIS B 0601.

In the wafer holder of the present invention, when supporter 4 has ahollow cylindrical shape with a bottom and whereby space 5 is formed, itis preferred that a metal layer is formed on the surface of supporter 4as an electromagnetic shield layer, utilizing the space inside thesupporter 4. The electromagnetic wave generated by heater body 6 forheating chuck top 2 may affect wafer inspection as noise, and when ametal layer is formed on supporter 4, it is possible to intercept(shield) the electromagnetic wave.

The method of forming the metal layer (electromagnetic shield layer) isnot specifically limited, and by way of example, a conductive pasteprepared by adding glass frit to metal powder of silver, gold, nickel orcopper may be applied using a brush and burned, metal such as aluminumor nickel may be thermally sprayed, or the layer may be formed byplating. Combination of these methods is also possible and, by way ofexample, metal such as nickel or the like may be plated after burningthe conductive paste, or plating may be done after thermal spraying.Among these methods, plating is preferred, as it has high contactstrength and is highly reliable. Further, thermal spraying is preferredas it allows formation of the metal film at a relatively low cost.

As another method of forming the metal layer (electromagnetic shieldlayer), a conductor may be provided on at least a part of the surface ofsupporter 4. Specifically, a conductor having a circular tube shape maybe attached on a side surface of supporter 4. The material used here isnot specifically limited, as long as it is a conductor. By way ofexample, metal foil or a metal plate of stainless steel, nickel,aluminum or the like may be used. Metal foil of the material mentionedabove is formed to have a circular tube shape of a size larger than theouter diameter of supporter 4, and it may be attached on the sidesurface of supporter 4.

Further, at the bottom surface portion of supporter 4, metal foil or ametal plate may be attached, and by connecting this to the metal foil ormetal plate attached to the side surface, the effect of shielding theelectromagnetic wave can be enhanced.

When the wafer holder of the present invention has space 5, the metalfoil or metal plate may be attached inside the space 5, and byconnecting this to the metal foil or metal plate attached to the sidesurface and the bottom surface of supporter 4, the effect of shieldingthe electromagnetic wave can be enhanced. By adopting the method ofattaching metal foil or a metal plate, the electromagnetic wave can beshielded at a lower cost than when plating is provided or a conductivepaste is applied. Though the method of fixing the metal foil or themetal plate to supporter 4 is not specifically limited, it may beattached using, for example, metal screws. Further, the metal foil orthe metal plates on the bottom surface and on the side surface may beintegrated beforehand and then fixed on supporter 4.

It is preferred that a metal layer (electromagnetic shield layer) forshielding the electromagnetic wave is also formed between heater body 6heating chuck top 2 and chuck top 2. The electromagnetic shield layerhas a function of cutting off noise such as electromagnetic wave orelectric field generated at heater body 6 and the like that mayinfluence probing of the wafer. Though the noise does not have muchinfluence on the measurement of common electric characteristics, it hasparticularly significant influence on the measurement of high-frequencycharacteristics of the wafer. The electromagnetic shield layer may beformed, for example, by inserting metal foil between heater body 6 andchuck top 2. It is preferred that the electromagnetic shield layer isinsulated from chuck top 2 and heater body 6. Though the metal foil tobe used here is not specifically limited, foil of stainless steel,nickel or aluminum is preferred, as heater body 6 is heated to thetemperature of about 200° C. For forming the electromagnetic shieldlayer, a method similar to the method of forming a meal layer on theside surface of supporter 4 described above may be used, and as anotherexample, metal foil may be inserted between heater body 6 and chuck top2.

Further, it is preferred that an insulating layer is provided betweenthe electromagnetic shield layer and chuck top 2. The insulating layerserves to cut off noise that affects inspection of the wafer, such asthe electromagnetic wave or electric field generated at heater body 6and the like. The noise particularly has significant influence onmeasurement of high-frequency characteristics of the wafer, and thenoise does not have much influence on the measurement of normal electriccharacteristics. Though most of the noise generated at the heater body 6is shielded by the electromagnetic shield layer, in terms of electriccircuit, a capacitor is formed between chuck top conductive layer 3formed on the wafer-mounting surface of chuck top 2 and theelectromagnetic shield layer when chuck top 2 is an insulator, orbetween chuck top 2 itself and heater body 6 when chuck top 2 is aconductor, and the capacitor may have an influence as a noise at thetime of inspecting the wafer. In order to reduce the influence, it ispreferred to form the insulating layer between the electromagneticshield layer and chuck top 2.

By controlling the resistance value, dielectric constant and capacitanceof the insulating layer, the noise at the time of inspection cansignificantly be reduced. Specifically, it is preferred that theresistance value of the insulating layer is at least 1×10⁷Ω. When theresistance value is smaller than 1×10⁷Ω, small current flows to chucktop conductive layer 3 because of the influence of heater body 6, whichsmall current possibly becomes noise and affects inspection. When theresistance value is at least 1×10⁷Ω, the small current can sufficientlybe reduced not to affect inspection. Recently, circuit patterns formedon wafers have been miniaturized, and therefore, it is necessary toreduce such noise as much as possible. In order to further improvereliability, it is preferred to set the resistance value of theinsulating layer to at least 1×10¹⁰Ω.

Further, when chuck top 2 is an insulator, capacitance between chuck topconductive layer 3 and the electromagnetic shield layer, or when chucktop 2 is a conductor, the capacitance between chuck top 2 itself and theelectromagnetic shield layer, should preferably be at most 5000 pF. Whenthe capacitance exceeds 5000 pF, the influence of the insulating layeras a capacitor would be too large, possibly causing noise and affectinginspection. Capacitance of at most 1000 pF is particularly preferred, asit enables inspection free of noise influence of even a miniaturizedcircuitry.

Further, it is preferred that the dielectric constant of the insulatinglayer is at most 10. When the dielectric constant of the insulatinglayer exceeds 10, charges tend to be stored more easily between theelectromagnetic shield layer sandwiching the insulating layer and chucktop 2, which might possibly be a cause of noise generation.Particularly, as the wafer circuits have been much miniaturized in thesedays, it is preferable to reduce noise, and therefore, dielectricconstant should preferably be at most 4 and more preferably at most 2.Setting small the dielectric constant of the insulating layer ispreferred, as the thickness of the insulating layer necessary forensuring the resistance value and the capacitance described above can bemade thinner, and hence, thermal resistance posed by the insulatinglayer can be reduced.

The thickness of the insulating layer should preferably be at least 0.2mm. In order to reduce the size of the device and to maintain good heatconduction from heater body 6 to chuck top 2, the thickness of theinsulating layer should be small. When the thickness of the insulatinglayer becomes smaller than 0.2 mm, however, defects in the insulatinglayer itself or problems in durability would be generated. It is morepreferred that the thickness of the insulating layer is at least 1 mm,because such a thickness prevents the problem of durability and ensuresgood heat conduction from the heater body 6. Though there is no specificupper limit of the thickness of the insulating layer, preferably it isat most 10 μm. When the thickness exceeds 10 mm, though the noisecutting effect is good, the time of conduction of heat generated byheater body 6 to chuck top 2 and to the wafer becomes too long, andhence, it possibly becomes difficult to control the heating temperature.Though it depends on the conditions of inspection, the thickness of theinsulating layer of at most 5 mm is preferred, as temperature control isrelatively easy.

The thermal conductivity of the insulating layer is preferably at least0.5 W/mK, in order to realize good heat conduction from heater body 6 asdescribed above. Thermal conductivity of at least 1 W/mK is preferred,as heat conduction is further improved. It is preferred that thediameter of the insulating layer, that is, the area for forming theinsulating layer, is the same or larger than the area for forming theelectromagnetic shield layer or heater body 6. When the diameter of theinsulating layer is smaller than the area for forming theelectromagnetic shield layer or heater body 6, noise may possibly enterfrom a portion not covered with the insulating layer.

The material for the insulating layer has only to satisfy thecharacteristics described above and have heat resistance sufficient towithstand the inspection temperature, and ceramics or resin may be used.Of these, resin such as silicone resin or the resin having fillerdispersed therein, and ceramics such as alumina, may suitably be used.The filler dispersed in the resin serves to improve heat conduction ofthe resin. Any material having no reactivity to the resin may be used asthe filler, and by way of example, substances such as boron nitride,aluminum nitride, alumina and silica may be available.

A specific example of the insulating layer will be described in thefollowing. First, as the material, silicone resin having boron nitridedispersed therein is used. The material has thermal conductivity ofabout 5 W/mK, and dielectric constant of 2. When the silicone resin withboron nitride dispersed is inserted as the insulating layer between theelectromagnetic shield layer and chuck top 2, and chuck top 2corresponds to a 12-inch wafer, it may be formed, for example, to havethe diameter of 300 mm. The thickness of the insulating layer may beselected dependent on the conditions of probing, and when the thicknessof the insulating layer is set to 0.25 mm, capacitance of 5000 pF can beattained and when the thickness is set to 1.25 mm or more, capacitanceof 1000 pF or lower can be attained. Volume resistivity of theinsulating layer is 9×10¹⁵ Ω·cm, and therefore, when the diameter is 300mm and the thickness is made at least 0.8 mm, the resistance value of atleast 1×10¹² Ω can be attained. Therefore, when the thickness of theinsulating layer is made at least 1.25 mm, an insulating layer havingsufficiently low capacitance and sufficiently high resistance value canbe obtained.

Further, it is preferred that a guard electrode layer is providedbetween chuck top 2 and the electromagnetic shield electrode layer, withan insulating layer interposed. By connecting the guard electrode layerto the metal member formed on supporter 4, the noise that affectsmeasurement of the high-frequency characteristics of the wafer canfurther be reduced. Specifically, in the present invention, by coveringsupporter 4 as a whole including heater body 6 with a conductor, theinfluence of noise at the time of measuring the characteristics of thewafer at a high frequency can be reduced.

Here, it is preferred that the resistance value of each of theinsulating layers between heater body 6 and the electromagnetic layer,between the electromagnetic layer and the guard electrode layer andbetween the guard electrode layer and chuck top 2 is at least 1×10⁷Ω.When the resistance value is smaller than 1×10⁷Ω, small current flows tochuck top conductive layer 3 because of the influence of heater body 6,which small current possibly becomes noise and affects inspection. Theresistance value of at least 1×10⁷Ω is preferred, as the small currentcan sufficiently be reduced not to affect inspection. Recently, circuitpatterns formed on wafers have been miniaturized, and therefore, it isnecessary to reduce such noise as much as possible. When the resistancevalue of the insulating layer is set to at least 1×10¹⁰Ω, a structure ofhigher reliability can be realized.

Further, when chuck top 2 is an insulator, capacitance between chuck topconductive layer 3 and the guard electrode layer, and between chuck topconductive layer 3 and the electromagnetic shield layer, or when chucktop 2 is a conductor, the capacitance between chuck top 2 itself and theguard electrode layer, and between chuck top 2 and the electromagneticshield electrode layer, should preferably be at most 5000 pF. When thecapacitance exceeds 5000 pF, the influence of the insulating layer as acapacitor would be too large, possibly becoming noise and affectinginspection. As the wafer circuits have been miniaturized as describedabove, capacitance of at most 1000 pF is particularly preferred, as itenables good probing.

A more specific example for forming the guard electrode layer inaccordance with the present invention will be described. By way ofexample, as the insulating layer, silicone resin having boron nitridedispersed therein is used as the insulating layer. The insulating layerhas the dielectric constant of 2. When the silicone resin with boronnitride dispersed is inserted as the insulating layer between theelectromagnetic shield layer and the guard electrode layer, or betweenthe guard electrode layer and chuck top 2, and the chuck top correspondsto a 12-inch wafer, it may be formed, for example, to have the diameterof 300 mm. Here, when the thickness of the insulating layer is set to0.25 mm, capacitance of 5000 pF can be attained. When the thickness isset to at least 1.25 mm, capacitance of 1000 pF or lower can beattained. Volume resistivity of the insulating layer is 9×10¹⁵ Ω·cm, andtherefore, when the diameter is 300 mm and the thickness is made atleast 0.8 mm, the resistance value of about 1×10¹²Ω can be attained.Though the thickness of the insulating layer may be selected dependenton the conditions of probing, the insulating layer has thermalconductivity of about 5 W/mK and, therefore, when the thickness of theinsulating layer is made at least 1.25 mm, good capacitance and goodresistance value can both be attained.

When the wafer holder in accordance with the present invention has space5, a cooling module 9 may be provided in space 5 inside supporter 4 ofwafer holder 800 as shown in FIG. 17. When it becomes necessary to coolchuck top 2, cooling module 9 is brought into contact with chuck top 2from the side opposite to the wafer-mounting surface and removes heattherefrom, so that chuck top 2 is cooled rapidly and the throughput canbe improved.

As the material of cooling module 9, aluminum, copper and an alloy ofthese are preferred, because they have high thermal conductivity andcapable of removing heat quickly from chuck top 2. It is also possibleto use stainless steel, magnesium alloy, nickel or other metalmaterials. On a surface of cooling module 9, a metal film formed of amaterial such as nickel, gold, silver or the like may be formed by amethod of plating, thermal spraying or the like, to add oxidationresistance. Among these materials, nickel-plated aluminum ornickel-plated copper is particularly preferred as cooling module 9, asit has superior oxidation resistance and high thermal conductivity andis relatively inexpensive.

Alternatively, ceramics may be used as the material for cooling module9. Among ceramics, aluminum nitride and silicon carbide are preferred asthey have high thermal conductivity and are capable of removing heatquickly from chuck top 2. Further, silicon nitride and aluminumoxynitride are preferred, as they have high mechanical strength andsuperior durability. Oxide ceramics such as alumina, cordierite andsteatite are preferred as they are relatively inexpensive. The materialfor cooling module 9 may be arbitrarily selected in consideration ofintended use, cost and the like.

A coolant may be caused to flow in cooling module 9. Causing the coolantflow is preferred, as the heat transferred from chuck top 2 to coolingmodule 9 can quickly be removed and the cooling rate of chuck top 2 canbe improved. Types of the coolant may be liquid such as water,Fluorinert or Galden, or gas such as nitrogen, air or helium. When thetemperature of use is always 0° C. or higher, water is preferredconsidering magnitude of specific heat and cost, and when it is cooledbelow zero, Galden is preferred considering specific heat.

As the method of forming the passage for the coolant flow, two platesmay be prepared, for example, and the passage may be formed by machineprocessing on one or both of the plates. Specifically, flow passages areformed on the surfaces of two cooling plates formed of aluminum, forexample, and in order to improve corrosion resistance and oxidationresistance, entire surfaces are nickel-plated, and thereafter, the twoplates are joined by means of screws or welding. At this time, a sealingmember such as an O-ring may preferably be inserted around the joinedportion of the passage, to prevent leakage of the coolant.

As another method of forming the flow passage, a pipe through which thecoolant flows may be attached to a cooling plate formed of aluminum orcopper. Here, in order to increase contact area between the coolingplate and the pipe, it is preferred that the cooling plate is processedto have a counter-sunk trench of an approximately the samecross-sectional shape as the pipe and the pipe is arranged in thetrench, or a flat-shaped portion is formed on a portion of the sidesurface of the pipe along the longitudinal direction and that flatportion is fixed on the cooling plate. By these methods, the pipe can bein close contact on the cooling plate, and therefore, cooling efficiencycan further be enhanced. As to the method of fixing the metal plate andthe pipe, screw fixing using a metal band, welding or brazing may beavailable. A deformable substance such as resin may be inserted betweenthe cooling plate and the pipe. Then, tight contact between the two isattained and cooling efficiency can be enhanced.

Specifically, two copper plates (oxygen-free copper) are prepared as thecooling plates, and the passage through which water as a coolant flowsis formed by machine processing or the like on one of the copper plates.The other copper plate and a pipe formed of stainless steel at an inletof the coolant are simultaneously joined by brazing. In order to improvecorrosion resistance and oxidation resistance of the joined coolingplates, the entire surface is nickel-plated, and thus, cooling module 9is formed.

As another approach, a pipe through which the coolant flows is attachedto a cooling plate such as an aluminum plate or copper plate, wherebycooling module 9 may be formed. In this case, by forming a counter-sunktrench having a shape close to the cross-sectional shape of the pipe torealize close contact with the pipe, cooling efficiency can further beincreased. Further, in order to improve tight contact between thecooling pipe and the cooling plate, thermally conductive resin, ceramicsor the like may be inserted as an intervening layer.

At the time of heating chuck top 2, if cooling module 9 can be separatedfrom chuck top 2, efficient temperature elevation of chuck top 2 becomespossible, and from the viewpoint of higher rate of temperature increase,it is preferred that cooling module 9 is movable. As a method ofrealizing mobile cooling module 9, an elevating mechanism 10 such as anair cylinder may be used as shown in FIG. 17. This approach is preferredas the cooling rate of chuck top 2 can significantly be improved and thethroughput can be increased. Cooling module 9 does not bear the load ofprobe card, and therefore, it is free from the problem of deformationcaused by the load. Further, this approach is preferred as the coolingperformance is better than air cooling.

On the other hand, when the cooling rate of chuck top 2 is of highimportance, cooling module 9 may be fixed on chuck top 2. Specifically,as shown in FIG. 18, heater body 6 may be provided on a side opposite tothe wafer-mounting surface of chuck top 2 of wafer holder 900, andcooling module 9 may be fixed on a lower surface of heater body 6. Asanother arrangement, as shown in FIG. 19, cooling module 9 is directlyprovided on a lower surface opposite to the wafer-mounting surface ofchuck top 2 of wafer holder 1000, and on a lower surface thereof, heaterbody 6 is fixed. Here, it is also possible to insert a deformable andheat-resistant soft material having high thermal conductivity betweenthe side opposite to the wafer-mounting surface of chuck top 2 andcooling module 9. In this case, the heater body may be fixed on thelower surface of the cooling module. By providing the soft materialbetween chuck top 2 and cooling module 9 that can moderate warp orparallelism of the two, it becomes possible to enlarge the contact area,and the original cooling performance of the cooling module 9 can morefully be exhibited, realizing higher cooling rate.

No matter in which arrangement the cooling module 9 is formed, themethod of fixing cooling module 9 is not specifically limited and, byway of example, it may be fixed by a mechanical method such as screwfixing or clamping. When chuck top 2, cooling module 9 and heater body6, and further an insulated heater, if any is provided, are to be fixedtogether by screws, three or more screws are preferred as tight contactbetween each of the members can be improved, and six or more screws aremore preferable.

Further, in the structure described above, cooling module 9 may bemounted inside the space 5 of supporter 4, or cooling module 9 may bemounted on supporter 4 and chuck top 2 may be mounted thereon. No matterwhich method is adopted, cooling rate can be increased as compared withthe example having mobile cooling module 9, as chuck top 2 and coolingmodule 9 are fixed together. Further, as cooling module 9 is mounted onsupporter 4, contact area of cooling module 9 with chuck top 2 isincreased, and hence, the chuck top can more rapidly be cooled.

When cooling module 9 fixed on chuck top 2 can be cooled by a coolant,it is preferred that the flow of coolant to cooling module 9 is stoppedwhen the temperature of chuck top 2 is increased or when it is kept at ahigh temperature. In that case, the heat generated by heater body 6 isnot removed by the coolant, and whereby efficient temperature increaseor maintenance of high temperature of chuck top 2 becomes possible.Naturally, chuck top 2 can be cooled efficiently by causing the coolantto flow again at the time of cooling.

Further, chuck top 2 itself may be formed as the cooling module, byproviding a passage through which the coolant flows inside chuck top 2and whereby integrating the chuck top and the cooling module. In thatcase, the time for cooling can further be reduced than when coolingmodule 9 is fixed on chuck top 2. As a structure of chuck top 2 for thisapproach, the following example may be available. Namely, chuck topconductive layer 3 is formed on one surface of one of two members toprovide the wafer-mounting surface, a passage for the coolant flow isformed on the opposite surface, and the other one of the members isintegrated by brazing, glass fixing or screw fixing, on the surfacehaving the passage formed thereon, whereby chuck top 2 is completed.Alternatively, a passage may be formed on one surface of said the othermember, and the member may be integrated with said one member on thesurface having the passage formed thereon, or passages may be made bothon the one and the other members, and the members may be integrated onthe surfaces having the passages formed thereon. It is preferred thatthe difference in thermal conductivity of the one and the other membersis as small as possible, and ideally, the members are preferably formedof the same material.

When chuck top 2 integrated with the cooling module is used, as thematerial for chuck top 2, ceramics or metal-ceramics composite may beused, or metal may be used. Metal is advantageous in that it isinexpensive as compared with ceramics or metal-ceramics composite, andit allows easy processing and hence the passage can be formed easily.When the chuck top of metal is used, however, it is preferred to providea plate 11 for preventing deformation as shown in wafer holder 1100 ofFIG. 20 and wafer holder 1200 of FIG. 21, on the side opposite to thewafer-mounting surface of chuck top 2, as it is much susceptible todeformation. In this case also, it is necessary to form a passage forthe coolant to flow inside chuck top 2, and therefore, the difference inthermal expansion coefficient between the material of the portion forforming the passage and other portions of chuck top 2 should preferablyas small as possible, and it is more preferable that the materials arethe same.

It is preferred that the plate 11 for preventing deformation has Young'smodulus of at least 250 GPa, similar to ceramics or metal-ceramicscomposite material used as the material for chuck top 2. Plate 11 forpreventing deformation may be inserted between chuck top 2 and supporter4 of wafer holder 1100 as shown in FIG. 20 in a state integrated withchuck top 2, or it may be housed in space 5 of supporter 4 of waferholder 1200 as shown in FIG. 21. Chuck top 2 and plate 11 for preventingdeformation may be fixed by a mechanical method such as screw fixing, ormay be fixed by a method such as blazing or glass fixing. Efficientheating and cooling is possible by not causing coolant to flow throughthe cooling module when chuck top 2 is heated or kept at a hightemperature and causing the coolant to flow only at the time of coolingchuck top 2, as in the example in which the cooling module is fixed onchuck top 2.

In a structure in which the cooling module is integrated within chucktop 2, the electromagnetic shield layer or the guard electrode layer maybe formed as needed, as in the example in which chuck top 2 and coolingmodule 9 are formed as separate members. In this case, insulated heaterbody 6 may be covered with metal, a guard electrode layer may be formedwith an insulating layer interposed, and between the guard electrodelayer and chuck top 2, an insulating layer may be formed.

Further, when chuck top 2 formed of metal is used and plate 11 forpreventing deformation is arranged on chuck top 2, again, it is possibleto form the electromagnetic shield layer or the guard electrode layer.By way of example, on a surface opposite to the wafer-mounting surfaceof chuck top 2, insulated heater body 6 is arranged, heater body 6 iscovered by a metal layer (electromagnetic shield layer), and thereafter,plate 11 for preventing deformation is arranged, and heater body 6, theelectromagnetic shield layer and plate 11 for preventing deformation maybe fixed integrally on chuck top 2. When the guard electrode is to beformed, the insulated heater body 6 described above is covered withmetal, the guard electrode is formed with an insulating layerinterposed, an insulating layer is formed between the guard electrodeand chuck top 2, and plate 11 for preventing deformation is formed, andthe heater body 6, the electromagnetic shield layer, the guard electrodeand plate 11 for preventing deformation may be fixed integrally to chucktop 2.

As for the method of mounting chuck top 2 integrated with the coolingmodule on supporter 4, the cooling module portion 9 may be place in thespace formed in supporter 4, or as in the case in which chuck top 2 andcooling module 9 are fixed by screws, it may have a structure that isarranged at the cooling module portion on supporter 4.

Next, an example in which the base portion and the circular tube portionof supporter 4 are formed integrally will be described with reference toFIGS. 22 to 29. Wafer holder 1300 has chuck top 2 having chuck topconductive layer 3, and supporter 4 supporting chuck top 2, and hasspace 5 at a portion between chuck top 2 and supporter 4. In waferholder 1300, supporter 4 has a structure in which the base portion andthe circular tube portion are formed integrally. As it has space 5, theheat insulating effect can be enhanced.

Even when supporter 4 has a structure having the base portion and thecircular tube portion formed integrally, the structure near theelectrode portion such as shown in FIG. 23, which is an enlargement ofthe portion surrounded by a circle of wafer holder 1300 of FIG. 22, forexample, can be formed in a preferable manner. Further, as in thestructure in which supporter 4 has separate base portion 41 and circulartube portion 42, it is possible to provide heater body 6 and support rod8 such as shown in wafer holder 1400 of FIG. 24.

Further, it is also possible to provide cooling module 9 such as shownin wafer holder 1500 of FIG. 25. Cooling module 9 may be made movable bycombining an elevating mechanism 10 such as shown in FIG. 25, or it maybe fixed on a lower surface of heater body 6 as cooling module 9 ofwafer holder 1600 shown in FIG. 26. As another arrangement, coolingmodule 9 may be directly attached to the lower surface opposite to thewafer-mounting surface of chuck top 2, and heater body 6 may be fixed onthe lower surface thereof, as cooling module 9 of wafer holder 1700shown in FIG. 27.

Further, by providing plate 11 for preventing deformation as shown inwafer holder 1800 of FIG. 28 or wafer holder 1900 of FIG. 29, it becomespossible to fix the electromagnetic shield layer or the guard layerintegrally with the chuck top.

The wafer holder in accordance with the present invention may bearranged in a container formed of stainless steel or the like, to be aheater unit. The heater unit may suitably be used as a wafer prober forinspecting electric characteristics of a wafer, and on the wafer prober,a driving system for moving the wafer holder may be provided. When thewafer holder of the present invention has characteristics such as highrigidity and high thermal conductivity, it may be applied, for example,to a handler apparatus or a tester apparatus, in addition to the waferprober. In any application, use of the wafer holder in accordance withthe present invention enables inspection of high accuracy withoutcausing contact failure to a semiconductor having minute circuitry.

EXAMPLES

As wafer holders, samples having the supporter of integral type basicshape (such as shown in FIG. 4) and the supporter of separate typeincluding the base portion and the circular tube portion (such as shownin FIG. 5) were fabricated as will be described later and listed inTable 1 below. Of these, three were in accordance with embodiments ofthe present invention, and three were comparative examples. These waferholders were each mounted on a wafer prober, and semiconductor waferswere inspected under the inspection conditions shown in Table 2 below.Respective wafer holders of the examples and comparative examples willbe described in detail in the following.

Example 1A

A wafer holder 300 having the structure shown in FIG. 4 with an integraltype supporter 4 was fabricated. As chuck top 2, an Si—SiC substratehaving the diameter of 310 mm and thickness of 15 mm was prepared. Onone surface of the substrate, a concentrical trench for vacuum chuckinga wafer and a through hole were formed, and nickel plating was appliedas chuck top conductive layer 3, and thus the wafer-mounting surface wasformed. Thereafter, the wafer-mounting surface was polished to attainsurface roughness Ra of 0.02 μm. Further, the contact surface betweenchuck top 2 and supporter 4 was polished and finished such that theamount of warp of the entire body was set to 10 μm and variation inthickness from the wafer-mounting surface to the contact surface withsupporter 4 was set to 45 μm, and thus, chuck top 2 was completed.

Next, as supporter 4, a cylindrical plate of mullite-alumina compositehaving the diameter of 310 mm and the height of 40 mm was prepared. Thecontact surface with chuck top 2 and the bottom surface of supporter 4were polished to have the variation in thickness of 46 μm from thebottom surface to the contact surface with chuck top 2, and thereafter,the contact surface with chuck top 2 was counter-bored to the innerdiameter of 290 mm and the depth of 3 mm, to form a cavity 51 forarranging heater body 6.

On chuck top 2 above, stainless steel foil insulated by mica wasattached as the electromagnetic shield layer, and further, heater body 6sandwiched by mica was attached. Heater body 6 was formed by etchingstainless steel foil in a prescribed pattern, and the electromagneticshield layer and heater body 6 were arranged at a position to be housedin cavity 51 provided in supporter 4. In supporter 4, a through hole wasformed in the similar manner as that shown in FIG. 7, and an electrodeline for power feeding passed through the through hole was connected toheater body 6. Further, on the side surface and the bottom surface ofsupporter 4, aluminum was thermally sprayed to be the electromagneticshield layer.

On supporter 4 described above, chuck top 2 having heater 6 and theelectromagnetic shield layer attached was mounted, and thus, waferholder 300 for a wafer prober having integral type supporter 4 shown inFIG. 4 was completed. The wafer holder was mounted on a wafer prober,and semiconductor wafers were inspected continuously for 10 hours, underthree different inspection conditions shown in Table 2 below, with theresults also shown in Table 2.

Comparative Example 1A

Wafer holder 300 having integral type supporter 4 shown in FIG. 4 wasfabricated in the similar manner as Example 1A except that the variationin thickness of chuck top 2 from the wafer-mounting surface to thecontact surface with supporter 4 was set to 54 μm and the variation inthickness of supporter 4 from the bottom surface to the contact surfacewith chuck top 2 was set to 53 μm. The obtained wafer holder 300 wasmounted on a wafer prober, and semiconductor wafers were inspectedcontinuously for 10 hours, under three different inspection conditionsshown in Table 2 below, with the results also shown in Table 2.

Wafer holder 300 having integral type supporter 4 shown in FIG. 4 wasfabricated in the similar manner as Example 1A except that the variationin thickness of chuck top 2 from the wafer-mounting surface to thecontact surface with supporter 4 was set to 45 μm and the variation inthickness of supporter 4 from the bottom surface to the contact surfacewith chuck top 2 was set to 54 μm. The obtained wafer holder 300 wasmounted on a wafer prober, and semiconductor wafers were inspectedcontinuously for 10 hours, under three different inspection conditionsshown in Table 2 below, with the results also shown in Table 2.

Comparative Example 3A

Wafer holder 300 having integral type supporter 4 shown in FIG. 4 wasfabricated in the similar manner as Example 1A except that the variationin thickness of chuck top 2 from the wafer-mounting surface to thecontact surface with supporter 4 was set to 53 μm and the variation inthickness of supporter 4 from the bottom surface to the contact surfacewith chuck top 2 was set to 44 μm. The obtained wafer holder 300 wasmounted on a wafer prober, and semiconductor wafers were inspectedcontinuously for 10 hours, under three different inspection conditionsshown in Table 2 below, with the results also shown in Table 2.

Example 2A

A wafer holder 400 having a separate type supporter 4 with base portion41 and circular tube portion 42 such as shown in FIG. 5 was fabricated.First, chuck top 2 was fabricated in the similar manner as in Example 1Aexcept that the variation in thickness of chuck top 2 from thewafer-mounting surface to the contact surface with supporter 4 was setto 46 μm.

Further, as components of supporter 4, a circular tube portion formed ofa mullite-alumina composite having the diameter of 310 mm, radialthickness of 10 mm and height of 30 mm, and a base portion formed of amullite-alumina composite having the diameter of 310 mm and thickness of15 mm were prepared. The circular tube portion and the base portion werepolished and finished such that the variation in thickness of circulartube portion 42 from the contact surface with the chuck top 2 to thecontact surface with the base portion 41 attained to 22 μm, and thevariation in thickness of base portion 41 from the bottom surface to thecontact surface with circular tube portion 42 attained to 23 μm.Circular tube portion 42 and base portion 41 were combined and supporter4 was obtained.

Wafer holder 400 having separate type supporter 4 shown in FIG. 5 wasfabricated in the similar manner as Example 1A including formation ofthe heater body and the electromagnetic shield layer, except thatsupporter 4 had the structure described above. Variation in thickness ofsupporter 4 from the bottom surface to the contact surface with chucktop 2 was 47 μm. The obtained wafer holder was mounted on a waferprober, and semiconductor wafers were inspected continuously for 10hours, under three different inspection conditions shown in Table 2below, with the results also shown in Table 2.

Example 3A

A wafer holder 400 having a separate type supporter 4 with base portion41 and circular tube portion 42 such as shown in FIG. 5 was fabricated.Here, wafer holder 400 having a separate type supporter 4 such as shownin FIG. 5 was fabricated in the similar manner as Example 2A except thatthe variation in thickness of chuck top 2 from the wafer-mountingsurface to the contact surface with supporter 4 was set to 9 μm, thevariation in thickness of circular tube portion 42 from the contactsurface with the chuck top 2 to the contact surface with the baseportion 41 was set to 5 μm, and the variation in thickness of baseportion 41 from the bottom surface to the contact surface with circulartube portion 42 was set to 4 μm. At this time, the variation inthickness of supporter 4 from the bottom surface to the contact surfacewith chuck top 2 was 10 μm.

The obtained wafer holder was mounted on a wafer prober, andsemiconductor wafers were inspected continuously for 10 hours, underthree different inspection conditions shown in Table 2 below, with theresults also shown in Table 2. Table 1 below collectively shows thevariation in thickness of the chuck top from the wafer-mounting surfaceto the contact surface with the supporter (that is, variation inthickness of the chuck top), the variation in thickness of the supporterfrom the bottom surface to the contact surface with the chuck top (thatis, variation in thickness of the supporter), the variation in thicknessof the circular tube portion from the contact surface with the chuck topto the contact surface with the base portion (that is, the variation inthickness of the circular tube portion), and the variation in thicknessof the base portion from the bottom surface to the contact surface withthe circular tube portion (that is, the variation in thickness of thebase portion) of the supporters in accordance with Examples 1A to 3A andComparative Examples 1A to 3A described above. TABLE 1 ExampleComparative Comparative Comparative 1A Example 1A Example 2A Example 3AExample 2A Example 3A Supporter Integral Integral type Integral Integraltype Separate Separate type (FIG. 4) type (FIG. 4) type type (FIG. 4)(FIG. 4) (FIG. 5) (FIG. 5) Chuck top 45 54 45 53 46 9 thicknessvariation (μm) Supporter 46 53 54 44 47 10  thickness variation (μm)Circular — — — — 22 5 tube portion thickness variation (μm) Base — — — —23 4 portion thickness variation (μm)

TABLE 2 Presence/absence of contact failure during inspection Load (kgf)150 150 200 Inspection  20 150 150 temperature (° C.) Example 1A notfailed failed failed Comparative failed failed failed Example 1AComparative failed failed failed Example 2A Comparative failed failedfailed Example 3A Example 2A not failed not failed failed Example 3A notfailed not failed not failed

As can be seen from the results shown above, when the variation inthickness of the chuck top and the variation in thickness of thesupporter were both adjusted to be at most 50 μm and the variation inthickness of the circular tube portion and the variation in thickness ofthe base portion were both adjusted to be at most 25 μm for thesupporter having the circular tube portion, deformation of the waferholder was not observed even when high load was applied, and contactfailure at the time of inspection could be avoided. Particularly, whenthe variation in thickness of the circular tube portion and thevariation in thickness of the base portion were both adjusted to be atmost 10 μm for the supporter having the circular tube portion,deformation of the wafer holder was not observed and contact failure atthe time of inspection could be avoided under severer inspectionconditions.

Example 1B

Alumina substrates having the purity of 99.5%, diameter of 305 mm andthe thickness shown in Table 3 were prepared. On the wafer-mountingsurface of each alumina substrate, concentrical trench for vacuumchucking and a through hole were formed, and the wafer-mounting surfacewas nickel-plated, to form the chuck top conductive layer. Thereafter,the chuck top conductive layer was polished, the amount of warp of theentire body was set to 10>m, surface roughness Ra was set to 0.02 μm,and the variation in thickness from the wafer-mounting surface to thecontact surface with the supporter was set to 10 μm, and thus a chucktop was obtained.

Next, a mullite-alumina composite of a cylindrical shape having thediameter of 305 mm and the thickness of 40 mm was prepared.

The contact surface with the chuck top and the bottom surface of thesupporter were polished and finished such that the variation inthickness from the bottom surface to the contact surface with the chucktop attained to 3 μm, and then, the contact surface with the chuck topwas counter-bored to the inner diameter of 285 mm and the thickness of20 mm. On each chuck top, stainless steel foil insulated by mica wasattached as the electromagnetic shield layer, and further, the heaterbody sandwiched by mica was attached. The heater body was formed byetching stainless steel foil in a prescribed pattern. In the supporter,a through hole for connecting an electrode for power feeding to theheater body was formed. Then, a metal layer was formed by thermalspraying of aluminum, on the side surface and the bottom surface of thesupporter.

Next, the chuck top having the heater body and the electromagneticshield layer attached was mounted on the supporter, and thus, a waferholder for a wafer prober was completed.

By applying electric power to the heater of wafer holder for the waferprober described above, the wafer was heated to 150° C., and probing wasdone continuously. The results are as shown in Table 3. Samples of whichratio of diameter to thickness was at least 5 and at most 100 had noproblem after continuous probing for 10 hours. Samples having the ratiosmaller than 5 had the chuck top warped after two hours, contact with aprobe pin was biased, and probing failed. In samples having the ratio ofdiameter to thickness exceeding 100, thermal uniformity of thewafer-mounting surface of the chuck top was unsatisfactory and accuratemeasurement was impossible.

Further, at the position of the diameter of 275 mm of the chuck top ofwafer holder for the wafer prober described above, a load (100 kg) wasapplied by using a load sensor having the diameter of 20 mm, and themagnitude of deflection was measured. The results are as shown in Table3. TABLE 3 Outer Max Amount of Diameter d Thickness t diameter/maxResult of continuous deflection No. (mm) (mm) thickness probing (μm) 1305 2 152.5 stopped after 2 hours 47.7 2 305 4 76.3 no problem after 10hours 18.4 3 305 10 30.5 no problem after 10 hours 7.8 4 305 15 20.3 noproblem after 10 hours 6.4 5 305 40 7.5 no problem after 10 hours 5.8 6305 70 4.4 thermal uniformity 4.2 problematic

As can be seen from Table 3, when the ratio of diameter to thicknessexceeded 100, the amount of deflection increased and accuratemeasurement was impossible.

Example 2B

Using the wafer holder for the wafer prober similar to sample No. 5 ofExample 1B except that the metal layer on the supporter was provided notby thermal spraying but by fixing metal foil of stainless steel withscrews, probing was done at a heated temperature of 150° C. as inExample 1B, and there was no problem after continuous probing for 10hours.

For comparison, the metal layer on the supporter was removed and probingwas done. Under the conditions of Example 1B, there was no problem aftercontinuous probing for 10 hours. However, probing related to highfrequency was affected by noise, and sometimes probing was notsuccessful. Further, probing was done with the electromagnetic shieldlayer removed. Then, because of the influence of noise that seemed to begenerated from the heater body, wafer characteristics could not bemeasured.

Example 3B

Si—SiC substrates having the diameter of 305 mm or 205 mm and thethickness shown in Table 4 were prepared. On the wafer-mounting surfaceof each Si—SiC substrate, concentrical trench for vacuum chucking and athrough hole were formed, and the wafer-mounting surface wasnickel-plated, to form the chuck top conductive layer. Thereafter, thechuck top conductive layer was polished and finished such that theamount of warp of the entire body was set to 10 μm, surface roughness Rawas set to 0.02 μm, and the variation in thickness from thewafer-mounting surface to the contact surface with the supporter was setto 10 μm, and thus a chuck top was obtained.

Next, mullite-alumina composite bodies of cylindrical shape having thediameter of 305 mm and 205 mm and the thickness of 40 mm were prepared.The contact surface with the chuck top and the bottom surface of thesupporter were polished, so that the variation in thickness from thebottom surface to the contact surface with the chuck top was finished to3 μm, and then, the bodies were counter-bored to the inner diameters of285 mm and 185 mm and the depth of 20 mm. On each chuck top, stainlesssteel foil insulated by mica was attached as the electromagnetic shieldlayer, and further, the heater body sandwiched by mica was attached. Theheater body was formed by etching stainless steel foil in a prescribedpattern. In the supporter, a through hole for connecting an electrodefor power feeding to the heater body was formed. Then, a metal layer wasformed by thermal spraying of aluminum, on the side surface and thebottom surface of the supporter.

Next, the chuck top having the heater body and the electromagneticshield layer attached was mounted on the supporter, and thus, a waferholder for a wafer prober was completed.

By applying electric power to the heater of wafer holder for the waferprober described above, the wafer was heated to 150° C., and probing wasdone continuously. The results are as shown in Table 4. Samples of whichratio of diameter to thickness was at least 5 and at most 100 had noproblem after continuous probing for 10 hours. Samples having the ratiosmaller than 5 had the chuck top warped after two hours, and contactwith a probe pin was biased, and probing failed. In samples having theratio of diameter to thickness exceeding 100, thermal uniformity of thewafer-mounting surface of the chuck top was unsatisfactory and accuratemeasurement was impossible.

Further, at a position of the diameter of 275 mm or 175 mm of the chucktop of wafer holder for the wafer prober described above, a load (100kg) was applied by using a load sensor having the diameter of 20 mm, andthe magnitude of deflection was measured. The results are as shown inTable 4. TABLE 4 Outer Max Amount of Diameter d Thickness t diameter/maxResult of continuous deflection No. (mm) (mm) thickness probing (μm) 7305 3 101.7 stopped after 3.4 hours 79.6 8 305 6 50.8 no problem after10 hours 18.4 9 305 10 30.5 no problem after 10 hours 6.8 10 305 25 12.2no problem after 10 hours 5.6 11 305 40 7.6 no problem after 10 hours4.8 12 305 75 4.1 thermal uniformity 4.6 unstable 13 205 2 102.5 stoppedafter 4.7 hours 60.4 14 205 4 51.3 no problem after 10 hours 12.9 15 2057 29.3 no problem after 10 hours 5.3 16 205 20 10.3 no problem after 10hours 4.8 17 205 30 6.8 no problem after 10 hours 4.7 18 205 50 4.1thermal uniformity 4.6 unstable

As can be seen from Table 4, when the ratio of diameter to thicknessexceeded 100, the amount of deflection increased and accuratemeasurement was impossible.

Example 4B

Using the wafer holder for the wafer prober similar to sample No. 9 ofExample 3B except that the metal layer on the supporter was provided notby thermal spraying but by fixing metal foil of stainless steel withscrews, probing was done at a heated temperature of 150° C. as inExample 3B, and there was no problem after continuous probing for 10hours.

For comparison, the metal layer on the supporter was removed and probingwas done. Under the conditions of Example 3B, there was no problem aftercontinuous probing for 10 hours. However, probing related to highfrequency was affected by noise, and sometimes probing was notsuccessful. Further, probing was done with the electromagnetic shieldlayer removed. Then, because of the influence of noise that seemed to begenerated from the heater body, wafer characteristics could not bemeasured.

Example 1C

A substrate formed of a composite of silicon and silicon carbide(Si—SiC) having the purity of 99.5%, diameter of 310 mm and thethickness of 10 mm was prepared. On the wafer-mounting surface of theSi—SiC substrate, concentrical trench for vacuum chucking and a throughhole were formed, and the wafer-mounting surface was nickel-plated, toform the chuck top conductive layer. Thereafter, the chuck topconductive layer was polished, the amount of warp of the entire body wasset to 10 μm, surface roughness Ra was set to 0.02 μm, and the variationin thickness from the wafer-mounting surface to the contact surface withthe supporter was set to 10 μm, and thus a chuck top was obtained.

Next, as the circular tube portion of the supporter, samples 1 to 8 ofmullite-alumina composite, having the diameter of 310 mm, inner diameterof 290 mm (that is, radial thickness of 10 mm), and the thickness shownin Table 5 were prepared. Further, as the base portion of the supporter,mullite-alumina composite bodies having the diameter of 310 mm and thethickness shown in Table 5 were prepared. These circular tube portionsand the base portions were fixed by screws, and supporter samples 1 to 8were obtained. The contact surface with the chuck top and the bottomsurface of the supporters were polished and finished until the variationin thickness from the bottom surface to the contact surface with thechuck top attained to 5 μm.

On the chuck top, stainless foil insulated by mica was attached as theguard electrode on the surface opposite to the wafer-mounting surface,and further, the heater body sandwiched by mica was attached. The heaterbody was formed by etching stainless steel foil in a prescribed pattern.The guard electrode and the heater body were arranged at a position tobe housed in the circular tube portion of the supporter. In the circulartube portion of the supporter, a through hole for connecting anelectrode for power feeding to the heater body was formed as shown inFIG. 7. Then, by thermal spraying of aluminum, on the side surface andthe bottom surface of the supporter, the guard electrode was provided.

On the supporter thus obtained, the chuck top having the heater body andthe electromagnetic shield layer attached was mounted, and the waferholder for the wafer prober shown in FIG. 5 was completed. The waferholders of samples 1 to 8 were mounted on wafer probers, andsemiconductors were inspected continuously for 10 hours under threedifferent conditions of inspection as shown in Table 6 below. Theresults are also shown in Table 6.

Example 2C

A mullite-alumina composite body of cylindrical shape having thediameter of 310 mm and the thickness of 60 mm was prepared. Portions tobe the contact surface with the chuck top and the bottom surface of thesupporter were polished, so that the variation in thickness from thebottom surface to the contact surface with the chuck top was finished to5 μm, and then the surface was counter-bored to have the diameter of 290mm and the depth of 30 mm, whereby a circular tube shape with a bottomwas obtained. Thus, a supporter of sample 9, which has the circular tubeportion having the thickness of 30 mm and the base portion having thethickness of 30 mm integrated and inseparable was formed.

The wafer holder of sample 9 was completed in the similar manner asExample 1C except for the supporter described above. The wafer holderwas mounted on the wafer prober, and a semiconductor was inspectedcontinuously for 10 hours under three different conditions of inspectionas shown in Table 6 below. The results are also shown in Table 6.

Example 3C

Sixteen pillars formed of alumina-mullite composite having the diameterof 10 mm and thickness of 5 mm were prepared. These 16 pillars werearranged uniformly as shown in FIG. 11 between the chuck top and thesupporter of the same type as fabricated in Example 2C described above,and thus, a supporter of sample 10 was obtained.

The wafer holder of sample 10 was completed in the similar manner asExample 1C except that 16 pillars described above were provided in thesupporter. The wafer holder was mounted on the wafer prober, andsemiconductors were inspected continuously for 10 hours under threedifferent conditions of inspection as shown in Table 6 below. Theresults are also shown in Table 6. TABLE 5 Thickness of various portionsof supporter (mm) Thickness ratio circular tube base (chuck topthickness t1) Sample portion t2 portion t3 pillar t4 t2/t1 t3/t1 t4/t1 11.5 5.5 — 0.15 0.55 — 2 10 10 — 1.0 1.0 — 3 30 30 — 3.0 3.0 — 4 45 95 —4.5 9.5 —  5* 0.9 30 — 0.09 3.0 —  6* 52 30 — 5.2 3.0 —  7* 30 4.7 — 3.00.47 —  8* 30 104 — 3.0 10.4 — 9 30 30 — 3.0 3.0 — 10  30 30 35 3.0 3.03.5(Note)In the Table, samples with * represent comparative examples

TABLE 6 Conditions and results of inspection (presence/absence ofcontact failure) Probe card load 100 kgf 200 kgf 200 kgf Inspection 100°C. 100° C. 200° C. temperature Sample 1 No contact failure Contactfailed Contact failed Sample 2 No contact failure Contact failed Contactfailed Sample 3 No contact failure Contact failed Contact failed Sample4 No contact failure Contact failed Contact failed Sample 5* Contactfailed Contact failed Contact failed Sample 6* Contact failed Contactfailed Contact failed Sample 7* Contact failed Contact failed Contactfailed Sample 8* Contact failed Contact failed Contact failed Sample 9No contact failure No contact failure Contact failed Sample 10 Nocontact failure No contact failure Contact failed(Note)In the Table, samples with * represent comparative examples

As can be seen from the results above, with the thickness of the chucktop t1 being 1.0, when the thickness t2 of the circular tube portion ofthe supporter was set to at least 0.1 and at most 5.0 and the thicknesst3 of the base portion was set to at least 0.5 and at most 10.0 withrespect to the thickness t1, the wafer holder did not deform even underhigh load, and contact failure could be avoided. Further, in the examplein which the pillars were provided, contact failure could be avoidedeven under the load of 200 kgf at 200° C., when the sum of thickness t4of the pillar and thickness t2 of the circular tube portion was set toat least 0.1 and at most 5.0 with the thickness t1 of the chuck topbeing 1.0

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein variation in thickness of said chuck top from said wafer-mounting surface to a contact surface with said supporter is at most 50 μm, and variation in thickness of said supporter from a bottom surface to a contact surface with said chuck top is at most 50 μm.
 2. The wafer holder according to claim 1, wherein said supporter has a structure including a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, with said circular tube portion and said base portion separated, and variation in thickness of said circular tube portion from a contact surface with said chuck top to a contact surface with said base portion is at most 25 μm, and variation in thickness of said base portion from a bottom surface to a contact surface with said circular tube portion is at most 25 μm.
 3. The wafer holder according to claim 1, wherein variation in thickness of said chuck top from said wafer-mounting surface to the contact surface with said supporter, variation in thickness of said supporter from the bottom surface to the contact surface with said chuck top, variation in thickness of said circular tube portion from the contact surface with said chuck top to the contact surface with said base portion, and variation in thickness of said base portion from the bottom surface to the contact surface with said circular tube portion are at most 10 μm.
 4. The wafer holder according to claim 1, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 5 and at most
 100. 5. The wafer holder according to claim 1, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 10 and at most
 50. 6. The wafer holder according to claim 1, wherein material of said chuck top is a composite of metal and ceramics.
 7. The wafer holder according to claim 1, wherein material of said chuck top is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide.
 8. The wafer holder according to claim 1, wherein material of said chuck top is ceramics.
 9. The wafer holder according to claim 1, wherein material of said supporter is ceramics or a composite of two or more ceramics.
 10. The wafer holder according to claim 9, wherein material of said supporter is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
 11. The wafer holder according to claim 1, wherein said supporter is formed of a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, thickness of said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0, and thickness of said base portion is at least 0.5 and at most 10.0 with thickness of said chuck top being 1.0.
 12. The wafer holder according to claim 1, wherein said circular tube portion and said base portion are formed integrally.
 13. The wafer holder according to claim 1, having a pillar between said circular tube portion and said base portion or between said circular tube portion and said chuck top, and a sum of thickness of said pillar and said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0.
 14. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 5 and at most
 100. 15. The wafer holder according to claim 14, wherein ratio of the maximum diameter to the maximum thickness of said chuck top is at least 10 and at most
 50. 16. The wafer holder according to claim 14, wherein material of said chuck top is a composite of metal and ceramics.
 17. The wafer holder according to claim 14, wherein material of said chuck top is a composite of aluminum and silicon carbide, or a composite of silicon and silicon carbide.
 18. The wafer holder according to claim 14, wherein material of said chuck top is ceramics.
 19. The wafer holder according to claim 14, wherein material of said supporter is ceramics or a composite of two or more ceramics.
 20. The wafer holder according to claim 19, wherein material of said supporter is any of alumina, silicon nitride, mullite, and a composite of alumina and mullite.
 21. A wafer holder having a chuck top mounting and fixing a wafer on a wafer-mounting surface, and a supporter supporting said chuck top, wherein said supporter is formed of a circular tube portion in contact with said chuck top and a base portion supporting said circular tube portion, thickness of said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0, and thickness of said base portion is at least 0.5 and at most 10.0 with thickness of said chuck top being 1.0.
 22. The wafer holder according to claim 21, wherein said circular tube portion and said base portion are formed integrally.
 23. The wafer holder according to claim 21, having a pillar between said circular tube portion and said base portion or between said circular tube portion and said chuck top, and a sum of thickness of said pillar and said circular tube portion is at least 0.1 and at most 5.0 with thickness of said chuck top being 1.0.
 24. A heater unit for a wafer prober, comprising the wafer holder according to claim
 1. 25. A heater unit for a wafer prober, comprising the wafer holder according to claim
 14. 26. A heater unit for a wafer prober, comprising the wafer holder according to claim
 21. 27. A wafer prober, comprising the heater unit according to claim
 1. 28. A wafer prober, comprising the heater unit according to claim
 14. 29. A wafer prober, comprising the heater unit according to claim
 21. 